Facility for producing reduced iron

ABSTRACT

In the method of producing reduced iron according to the invention, fine iron oxides and powdery solid reductants are mixed, compacted into sheet-like compacts, and charged onto the hearth of a reduction furnace for reduction while maintaining the temperature inside the furnace at not less than 1100° C. As the sheet-like compacts can be obtained by compacting mixture of raw material by use of rollers or the like, processing time is much shorter than the case of pelletization or agglomeration. A drying step is unnecessary since feeds are placed no the hearth via a feeder chute or the like. The method is carried out with ease by use of the facility according to the invention. High quality hot metal can be produced by charging reduced iron in hot condition obtained by the method described as above into a shaft furnace or a in-bath smelting furnace for melting at high thermal efficiency.

This application is a continuation of international applicationPCT/JP97/04091, filed on Nov. 10, 1997.

TECHNICAL FIELD

The present invention broadly relates to production of reduced iron, andproduction of hot metal therefrom. More particularly, the presentinvention is concerned with a method of and a facility for producingreduced iron by compacting fine iron oxides, for example, fine iron ore,iron-bearing dust, sludge, scale, and the like which are generated atsteel mills, in admixture with powdery solid reductants, for example,coal, charcoal, petroleum cokes, cokes, and the like, into sheet-likeshape without agglomerating aforesaid raw materials, and by chargingsheet-like compacts into a heated furnace for reduction at a hightemperature, and further, with a method of producing hot metal bycharging the reduced iron kept in a hot condition into a shaft furnaceor an in-bath smelting furnace.

BACKGROUND TECHNOLOGY

With recent growth in production of steel products by means of electricfurnaces, much attention has been drawn to a technology of obtainingferrous material as a feed therefor by solid reduction of iron ores.There has since been disclosed a process, representative of thetechnology, wherein solid metallized iron is produced by formingagglomerates, so-called "pellets", from fine iron ore in admixture withpowdery solid reductants, and then reducing iron oxides contained in thefine iron ore through heating of the agglomerates at a high temperature(reference: for example, specification of U.S. Pat. No. 3,443,931, andJapanese Patent Laid-open No. 7-238307).

The process of reducing fine iron ore as disclosed in U.S. Pat. No.3,443,931 described above comprises generally the following steps of:

1) forming green pellets by mixing fine iron ore with powdery solidreductants such as coal, coke, and the like,

2) removing water adhered to the green pellets by heating same in such atemperature range that combustible volatile constituents issuedtherefrom are not ignited,

3) reducing dried pellets by heating same at a high temperature to raisea metallization ratio, and

4) cooling metallized pellets before discharging same out of a furnace.

The conventional process of producing reduced iron as disclosed in U.S.Pat. No. 3,443,931 described above (for the sake of convenience,referred to as "pelletizing process" hereinafter) has fundamentalproblems as follows:

1) As an agglomerate (pellet) as merely agglomerated does not havesufficient physical strength to withstand handling during the process,it requires drying before charged into a reduction furnace. This entailsinstallation of a drying unit in addition to a pelletizing furnace ofcomplex construction, involving fairly high costs of operation andmaintenance thereof. Furthermore, owing to a longer time required in theprocess from a step of drying the pellet to completion of a reductionstep, production efficiency of the process is low, and it is difficultto hold down a cost of producing reduced iron.

2) It is impossible to avoid generation of particles outside apredetermined size range during the pelletizing process. As it isnecessary to recycle undersize particles to a mixing step, and to crushoversize particles before recycling to the mixing step, the productionefficiency is poor.

3) Iron oxides generated at steel mills such as iron-bearing dust,sludge, scale, and the like are among precious ferrous materials,however, these are often found in lumpy form when recovered, composed offine particles bonded together, or in a form too large as pellet feed asin the case of scales. Accordingly, for pelletizing these iron oxides ontheir own in place of iron ore fine, or in admixture with iron ore fine,it is necessary to pulverize them to a predetermined size beforehand,necessitating installation of a pulverizing apparatus.

It is known that in reduction reaction of pellets, the higher atemperature at which the reaction takes place, the more rapidly thereaction proceeds. Hence, it is essential to heat up the pellets to apredetermined temperature rapidly by increasing a warming rate in orderto improve productivity by increasing a reduction reaction rate. Theprocess disclosed in the Japanese Patent Laid-open No. 7-238307described above is characterized in that for a while after pellets arecharged into a furnace, an oxygen containing gas is supplied onto thesurface of the charged pellets, causing combustible matter issued fromthe pellets to be actively combusted so that a temperature on thesurface of pellets is elevated to an optimum temperature for reductionby heat of combustion.

The process disclosed in the Japanese Patent Laid-open No. 7-238307described above, however, belongs to a category of the pelletizingprocess consisting of steps of mixing, agglomeration, and drying, hardlysolving the problems of the pelletizing process described above.

A furnace provided with a horizontally rotatable hearth (referred to asrotary hearth hereinafter) for heating is drawing attention in producingthe reduced iron, and a same type furnace (referred to as rotary hearthfurnace hereinafter) is used in the process as disclosed in the U.S.Pat. No. 3,443,931.

The rotary hearth furnace is characterized by its low capital cost asopposed to the case of a rotary-kiln furnace which has been in practicaluse over many years, however, due consideration should be given tocharging of raw materials and discharging of a product since the hearthis horizontally rotated in the former case.

FIG. 1 is a schematic representation showing an example of conventionalprocesses of producing the reduced iron by use of the rotary hearthfurnace for heating of raw materials. As shown in the figure, fine ironore 3 crushed to a predetermined size by a crusher 1, and pulverizedcoal 4 prepared by a dryer 2 and crusher 1 with bentonite 5 as binderadded thereto are kneaded and mixed by a mixer 6 while water 7 and tar 8are further added thereto. Mixed raw materials thus obtained areagglomerated by a pelletizer 9 or double-roll compactor 10, transferredto a feeder 12 of the rotary hearth furnace 11, and charged into thefurnace, producing solid metallized iron by reducing iron oxides in theiron ore at a high temperature every time the rotary hearth 13 makes oneturn. The metallized iron obtained is discharged from a product outlet14. Reference numeral 15 denotes an exhaust outlet.

When the fine iron oxide and powdery solid reductants are kneaded andmixed after drying and crushing as necessary, a binder such as water,tar, theriac, organic resin, cement, slag, bentonite, quick lime,slightly burnt dolomite, or slaked lime is added thereto if need be.

The mixed raw materials are agglomerated into pellets in the shape of aball by a desk pelletizer, or briquettes by the double-roll compactor.As the mixed raw materials of a particle size, 0.1 mm or less indiameter, are suitable for pelletizing, and same of a particle size, 1mm or less, are for briquetting, the materials require priorpulverization to a predetermined size. In some cases, drying or curingtreatment is applied to the agglomerates (that is, pellets andbriquettes) to enhance physical strength thereof.

The agglomerates are sent to an upper part of the rotary hearth furnacevia a belt conveyer, and charged via a feeding chute into the furnace soas to be spread in a wide area on the surface of the rotary hearth andsmoothed out by a leveler. Subsequently, the agglomerates are heated andreduced while in rotation within the furnace, and turned into metallizediron.

The conventional process of producing reduced iron described above,however, has the following problem. That is, the agglomerates, due topowdering occurring thereto before charged into the rotary hearthfurnace, will turn into agglomerates composed of particles of variousdiameters while generating fines, and charged onto the rotary hearth insuch a condition. Then, generated fines are blown off by a combustinggas, and adhered in a molten condition to the wall of the furnace,causing troubles to facilities. In addition, the generated fines adherein a molten condition to the rotary hearth, erode the hearth and roughenthe surface of it.

Further, nonuniformity in firing results due to lack of uniformity inthe size of the agglomerates, leading to the need of lengthening afiring time required for producing reduced iron of 92% metallizationratio, lowering productivity in producing the reduced iron.

Addition of the binder described above for prevention of an adverseeffect of powdering of the agglomerates has been found effective to anextent, however, not successful in complete prevention of thepowerdering. Furthermore, use of organic binders, which are expensive,results in a higher cost of production while use of inorganic bindershaving a constituent other than iron, that is, a slag constituent, has adrawback of degrading the quality of the reduced iron.

As described in the foregoing, the conventional pelletizing process hasa number of problems.

Meanwhile, hot metal has been produced up to date primarily by the blastfurnace process. In the blast furnace process, lumpy ferrous rawmaterial and lumpy coke are charged into the furnace from the upper partthereof while hot blast is blown in through tuyeres provided in thelower part thereof so that the cokes are combusted, generating areducing gas at a high temperature whereby iron oxides, main constituentof the ferrous material, are reduced and melted.

There has recently been developed another method of producing hot metalwherein reduced iron is produced by reducing lumpy ferrous raw materialin a shaft reduction furnace, and the reduced iron in a hot condition ischarged into a carbon material fluidized bed type melting furnace fromthe upper part thereof for reduction and melting. This method hasalready been put to practical application.

Various methods of producing hot metal directly from fine iron ores havealso been developed. For example, in Japanese Patent Publication No.3-60883, there has been disclosed a process wherein agglomerates areformed of fine iron ore and pulverized carbon material, the agglomeratesare then prereduced in a rotary hearth furnace, and discharged at atemperature not less than 1000° C. into a smelting furnace having amolten metal bath therein while the pulverized carbon material is fedunder the surface of the molten bath, thereby reducing and melting theprereduced agglomerates in the smelting furnace. In this instance,off-gas discharged from the smelting furnace is recycled into the rotaryhearth furnace for use as fuel for prereduction.

The conventional technologies described above, however, have drawbacksas follows:

Firstly, the blast furnace process has a drawback of requiring lumpyferrous raw material and coke. In this process, cokes are formed in cokeovens through carbonization of coal, and only lumpy cokes are used afterscreening. Deposits of hard coking coal for use in making cokes areunevenly distributed in geographical terms. In addition, other majorproblems with the process are huge capital outlay required in replacingthe old coke ovens, and needs for prevention of air pollution caused byoperation of the coke ovens. With respect to ferrous raw material, fineiron ores need to be agglomerated into pellets or sinters for use in theprocess except the case where lumpy ores are used. In view of a tightsupply position of lumpy iron ore, and high costs of pellets, however,use of sinters has come to be in the mainstream of the steel industry'spractice in Japan, but countermeasures for prevention of air pollutioncaused by sintering operation poses a major problem to the industry.

In the process of producing hot metal in the shaft reduction furnace,coke is not required, however, the process has a problem of requiringlumpy iron ore as ferrous raw material as in the case of the blastfurnace process.

A process described in Japanese Patent Publication No. 3-60883 isconsidered effective, however, has a drawback that fine iron oxides andpowdery solid reductants need to be mixed and agglomerated before beingcharged into a reduction furnace.

In the course of agglomeration, particles outside a predetermined sizerange are inevitably generated as described hereinabove. Accordingly,undersize particles are sent straight to a mixing step while oversizeparticles need to be crushed before recycled to the mixing step,deteriorating efficiency of the process. In addition, since agglomeratesas merely agglomerated do not have sufficient strength to withstandhandling, the agglomerates need to be dried before charged into thereduction furnace, entailing installation of a drying unit in additionto an agglomeration plant. Costs of operation and maintenance thereofare also involved. All these factors add up the production cost ofreduced iron. Furthermore, time required for agglomeration and drying isrelatively long in comparison with that for reduction, adverselyaffecting the efficiency of a plant as a whole.

In the case of utilizing iron oxides generated at steel mills such asiron-bearing dust, sludge, scale, and the like, on their own or incombination with iron ores, these are often recovered in the form of "alump composed of fine particles bonded together", or in "shape too largeas pellet feeds" as in the case of mill scales. Accordingly, the ironoxides need to be pulverized beforehand to a predetermined size,necessitating installation of a pulverizing apparatus.

The present invention has been developed to provide a method of and afacility for production of reduced iron in a simple and inexpensive wayin place of the conventional pelletizing method, and further, to providea method of producing high quality hot metal efficiently and at a lowcost through a simple process using reduced iron obtained as above.

DISCLOSURE OF THE INVENTION

In a method according to the invention, an agglomeration step forferrous raw material and fuel (a step of agglomerating raw material suchas pelletization, and the like), and a drying step, which have beenconsidered essential for pre-reduction of raw material, are dispensedwith. More specifically, the method according to the invention ischaracterized in that fine ferrous raw material and powdery solidreductants are mixed with each other, compacted into sheet-like shapewithout agglomeration, and charged into a furnace, heated to not lessthan 1200° C., thereby reducing iron oxides.

The invention has features comprising a method of producing reduced iron(1), a facility for carrying out the method (2), and methods ofproducing hot metal from the reduced iron (3) and (4) describedhereinafter:

(1) A method of producing reduced iron from fine iron oxides comprisingthe steps of a) through d) as follows;

a) obtaining raw material mixture by mixing fine iron oxides withpowdery solid reductants,

b) compacting the raw material mixture into sheet-like compacts,

c) placing the sheet-like compacts on the hearth of a reduction furnace,and

d) reducing iron oxides contained in the sheet-like compacts by blowingfuel and oxygen-containing gas into a reduction furnace, and burning thefuel, combustible volatile constituents issued from the powdery solidreductants and the CO gas generated as a result of reduction of the ironoxides by the agency of the powdery solid reductants, so that atemperature inside the furnace is maintained at not less than 1100° C.

(2) A facility for carrying out the method (1) described abovecomprising;

a mixer for mixing the fine iron oxides with the powdery solidreductants,

a compactor for compacting the raw material mixture obtained through themixing step into the sheet-like compacts

a feeder for placing the sheet-like compacts on the hearth of thereduction furnace, and

a reduction furnace for reducing the iron oxides contained in thesheet-like compacts fed therein, said reduction furnace being a rotaryhearth furnace having a furnace body provided with a feeding inlet forthe sheet-like compacts, a discharge outlet for the reduced ironproduced through high temperature reduction of the iron oxides, and anexhaust outlet for off-gas generated therein, the hearth which isinstalled therein so as to be horizontally rotatable, and burners forcombusting the fuel after the fuel and the oxygen-containing gas areblown in;

(3) A method of producing hot metal from fine iron oxides aftercompletion of the steps a) through d) of the method (1) described above,comprising steps of e) through g) described below;

e) discharging the reduced iron obtained through the reduction step(pre-reduction step) described above and kept at not less than 500° C.from the reduction furnace (pre-reduction furnace),

f) reducing and melting the reduced iron in a hot condition dischargedthrough the discharge step described above by charging the reduced irontogether with lumpy carbon material and flux into a shaft furnace fromthe upper part thereof, having a carbon material bed therein, andtuyeres in the lower part thereof for oxygen containing gas blown intherethrough to combust the carbon material disposed in front thereof,generating reducing gas at a high temperature, so that hot metal andmolten slag are discharged through a tap hole provided in the lower partof the shaft furnace, and

g) recovering off-gases generated in the shaft furnace, and recycling apart of the off-gases into the pre-reduction furnace for use as a fuelfor pre-reduction.

(4) A method of producing hot metal from the fine iron oxides aftercompletion of the steps a) through d) of the method (1) described above,comprising steps of e) through g) described below:

e) discharging the reduced iron obtained through the reduction step(prereduction step) described above and kept at not less than 500° C.from the reduction furnace (prereduction furnace),

f) reducing and melting the reduced iron in a hot condition dischargedthrough the discharge step described above by charging the reduced irontogether with a carbon material and a flux into a in-bath smeltingfurnace from the upper part thereof, the in-bath smelting furnace havingmolten metal bath and molten slag bath therein, and through the bottomof which gas for agitation is blown into the molten metal bath forstirring up the molten metal bath and molten slag bath while oxygen isblown thereinto from the upper part thereof, so that hot metal andmolten slag are discharged through a tap hole provided in the lower partof the in-bath smelting furnace, and

g) recovering off-gases generated in the in-bath smelting furnace, andrecycling a part of the off-gases into the pre-reduction furnace for useas a fuel for pre-reduction.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration showing a conventional process ofproducing reduced iron by way of example.

FIG. 2 is a longitudinal section showing an example of compacting andfeeding apparatus.

FIG. 3 is a view illustrating a shape of a sheet-like compact by way ofexample.

FIG. 4 is a schematic view showing a facility for production of reducediron according to the invention, and a method of producing reduced ironusing the facility.

FIG. 5 is a longitudinal section of a rotary hearth furnace, showing avertical section against the direction of advance of the hearth,

FIG. 6 is a view illustrating the principal part of a feeding apparatusaccording to an embodiment of the invention.

FIG. 7 is a view illustrating an arrangement of a plurality ofdouble-roll compactors by way of example.

FIG. 8(a) is a sectional view showing a schematic illustration of theconstruction of the feeding apparatus according to an embodiment of theinvention.

FIG. 8(b) is a sectional view showing a schematic illustration of theconstruction of the feeding apparatus according to another embodiment ofthe invention.

FIG. 9 is a view illustrating the principal part of a compacting andfeeding apparatus according to another embodiment of the invention.

FIG. 10(a) is a top view of the rotary hearth.

FIG. 10(b) is a longitudinal sectional view of the vicinity of thedischarge outlet.

FIG. 11(a) is a top view illustrating an example of the method using apusher as a method of discharging reduced iron according to theinvention.

FIG. 11(b) is a cross-sectional view of FIG. 11(a) at section A--A.

FIG. 11(c) is a top view illustrating another example of the method.

FIG. 11(d) is a cross-sectional view of FIG. 11(c) at section B--B.

FIG. 12 is a view illustrating a method of removing reduced iron finesremaining on the hearth according to an embodiment of the invention.

FIG. 13 is a view illustrating a method of removing reduced iron finesremaining on the hearth according to another embodiment of theinvention.

FIG. 14 is a view illustrating a method of removing reduced iron finesand adhesive matter remaining on the hearth according to yet anotherembodiment of the invention.

FIG. 15 is a view illustrating a method of removing reduced iron finesand adhesive matter remaining on the hearth according to furtherembodiment of the invention.

FIG. 16 is a view illustrating a method of preventing reduced iron finesfrom remaining on the hearth according to an additional embodiment ofthe invention.

FIG. 17 is a schematic illustration showing a method of producing hotmetal in a shaft furnace, and a facility for carrying out the method.

FIG. 18 is a schematic illustration showing a method of producing hotmetal in a in-bath smelting furnace, and a facility for carrying out themethod.

FIG. 19 is a view illustrating a test furnace for high temperaturereduction used in carrying out a test for an example.

FIG. 19(a) is a vertical cross sectional view illustrating a testfurnace for high temperature reduction used in carrying out a test foran example.

FIG. 19(b) is a cross sectional view taken along arrow A--A in FIG.19(a).

FIG. 20 is a schematic illustration of a method of mixing and feedingraw material according to an embodiment of the invention.

FIG. 21 is a graph showing relationship between water in raw materialand metallization ratio based on the test results.

FIG. 22 is a graph showing relationship between content of Al₂ O₃ +SiO₂in iron ore and metallization ratio based on the test results.

FIG. 23 is a graph showing relationship between ratio of fine particlesbetween 0.1 and 1 mm in coal and metallization ratio based on the testresults.

BEST MODE OF CARRYING OUT THE INVENTION

A method of, and a facility for producing reduced iron, and a method ofproducing hot metal, according to the invention, are described in detailhereinafter.

The method of producing reduced iron according to the invention (theinvention referred to in (1) above) is a process wherein fine ironoxides are reduced at a high temperature by compacting a mixture of fineiron oxides and powdery solid reductants into a sheet-like shape,placing sheet-like compacts on the hearth of a reduction furnace,blowing fuel and oxygen containing gas into the reduction furnace, andburning the fuel, combustible volatile constituents (VM) issued from thepowdery solid reductants and the CO gas generated as a result ofreduction of the iron oxides by the agency of the powdery solidreductants, so that a temperature inside the furnace is maintained atnot less than 1100° C.

In this context, "fine iron oxides" refer to fine ferrous raw materialscontaining iron oxide as its main constituent, and more specifically, toaforesaid fine iron ore and iron-bearing wastes generated at steel millssuch as dust, sludge, scale, and the like. Each of these can be used onits own or in a mixture of two or more.

Then, "powdery solid reductants" refer to powders of a solid materialcontaining mainly carbon, such as coal, charcoal, petroleum cokes,cokes, and the like. Each of these can also be used on its own or in amixture of two or more.

Further, "sheet-like compacts" refer to a continuous band (referred toas "in a sheet-like form" hereinafter) formed by compacting a mixture offine iron oxides and powdery solid reductants. The sheet-like compactsin the form of a perfect sheet is preferable, but may have cracksoccurring thereto. The width of the sheet-like compacts may be selectedat option depending on the scale of the reduction furnace. Adequatethickness thereof is generally in the range of 10 to 20 mm.

There is no particular restriction on a type of the reduction furnaceused in carrying out the invention, however, the rotary hearth furnaceas illustrated in FIG. 1 shown hereinbefore, that is, the reductionfurnace provided with a horizontally rotatable hearth (rotary hearth) isadvisable because of its capability for continuous operation.

In the method of producing reduced iron according to the invention,firstly a mixture (mixture of raw materials) is prepared by mixing fineiron oxides with powdery solid reductants.

In mixing fine iron oxides with powdery solid reductants, some amount ofwater or binder (bentonite, lime, organic binders, emulsion, oil,surface-active agent, or the like), or both may be added. Thisfacilitates uniform and rapid mixing, and furthermore, formation of thesheet-like compacts.

Lime (burnt lime, limestone, or the like) may also be added foradjustment of basicity of slag constituent contained in the reducediron. This enables concentration of sulfur contained in off-gas emittedfrom the reduction furnace to be lowered. Use of limestone alsocontributes to improvement in a unit fuel consumption as the effect ofendothermic reaction accompanying decomposition of limestone iscompensated for during firing in the reduction furnace.

In the method according to the invention, there is no need ofagglomerating the mixture of raw materials, and accordingly, coarsecrushing of scales, and the like suffices the need, requiring nopulverization.

In the case of using dust containing zinc (Zn), and the like for the rawmaterial, a possibility of the quality of a product being degraded dueto residual zinc remaining in the reduced iron is a matter of concern,however, a metal of a low boiling point such as zinc is evaporated inthe furnace used in the method according to the invention which is keptat a high temperature, and discharged together with off-gas out of thefurnace. It is possible therefore not only to lower the content of suchmetals having a low boiling point as zinc, and the like remaining in thereduced iron product, improving the quality of the product, but also torecycle and use the metals which can be enriched in dust arrested by adust collecting equipment.

In the next step, the mixture of the fine iron oxides and powdery solidreductants is compacted into a sheet-like shape, and the sheet-likecompacts are placed on the hearth of the reduction furnace.

There is no particular restriction on a means of forming the sheet-likecompacts, however, use of a compacting method, particularly, by adouble-roll compactor described hereinafter is preferable from theviewpoint of simplicity of the compactor, easy formability, and highforming efficiency.

As shown in FIG. 2, with reference to which detailed description isgiven hereinafter, the mixture of the raw materials 16 is compacted intothe sheet-like shape by, for example, pairs of rolls 17, and placed onthe hearth 13.

The surface area (that is, area receiving heat) of the sheet-likecompact 18 can be enlarged when provided with projections on a surfaceopposite to a surface facing the hearth, for example, cutting grooves 21as shown in FIG. 3, restraining a decline in a warming rate of thesheet-like compact accompanying an increase in the thickness thereof.Further, as result of this, the weight of the raw materials loaded on aunit surface area of the hearth is increased, enhancing productivity.

Subsequently, iron oxides contained in the sheet-like compacts arereduced by blowing fuel and oxygen-containing gas into the reductionfurnace, and burning the fuel, combustible volatile constituents issuedfrom the powdery solid reductants and the CO gas generated as a resultof reduction of the iron oxides by the agency of the powdery solidreductants, so that a temperature inside the furnace is maintained atnot less than 1100° C., thus producing the reduced iron.

Ordinary fuel such as natural gas, heavy oil, or the equivalent is usedfor a fuel used in the process. Combustible gases are discharged asoff-gas from a smelting furnace (a shaft furnace or a in-bath smeltingfurnace) operated in later steps of the process, and may be used for thefuel.

For the oxygen-containing gas, air or gas containing oxygen inconcentration equivalent to or somewhat higher than that for air maypreferably be used.

A temperature in the furnace for high temperature reduction is set atnot less than 1100° C. Reduction will proceed even at a temperaturebelow 1100° C., however, a reduction rate is so low in such atemperature range that such a practice is undesirable for industrialproduction. It is desirable to maintain a temperature in the furnace onthe order of 1200 to 1400° C. in order to attain a sufficiently highrate of reduction because temperatures at a sheet-like compact becomelower than the temperature in the furnace due to the effect ofendothermic reaction of the iron oxides during reduction.

The temperature in the reduction furnace, however, is to be adjusteddepending on a condition of progress in reduction, nature of ferrous rawmaterial and powdery solid reductants, a mixing ratio and the like. Morespecifically, when raw materials charged into the furnace are still at alow temperature in a period immediately after charging of the rawmaterials, it is advantageous to raise a temperature of the charged rawmaterials by maintaining the temperature in the furnace on a higher sidefrom the viewpoint of promoting reduction. Further, since a meltingpoint of the charged raw materials varies depending on, for example,composition of gangues contained in iron ores, and same of ash contentin a coal, due care should be exercised to prevent flowing out of meltedraw materials by controlling the temperature in the furnace providedthat an adequate amount of a liquid phase formed in the charged rawmaterials is beneficial for heat transmission and promotion of reaction,and should therefore be made active use of.

In reducing iron oxides at a high temperature, it is desirable to raisea temperature of the sheet-like compacts rapidly up to an optimumreduction temperature in order to shorten time required for reduction.To this end, in heating the sheet-like compacts, oxygen-containing gasmay be supplied to the surface of the sheet-like compacts to combust acombustible volatile constituents issued therefrom on the surfacethereof until issuing of the volatile constituents is substantiallyceased, and may continue heating so that the temperature in the furnacereaches to not less than 1100° C., preferably, not less than 1200 to1400° C. after issuing of the volatile constituents is ceased.

Then, for preventing reduced iron from sticking to the hearth in thereduction furnace, a method may be adopted wherein the powdery solidreductants are spread to form a thin film over the hearth in thereduction furnace, and the sheet-like compacts are placed on the thinfilm.

In the method of producing reduced iron according to the invention, thesheet-like compacts are obtained by simply compacting the mixture of rawmaterials with a roller or the like as described above, and accordingly,processing time is much shorter than that for pelletization oragglomeration while operation and maintenance of a compacting apparatusare carried out with ease. Further, pellets as merely agglomerated donot have sufficient strength, and need to be dried to increase physicalstrength thereof, however, the sheet-like compacts do not undergodisintegration without going through a drying step provided that theseare placed on the hearth via the support roller or the like as shown inFIG. 2. Even in case that the sheet-like compacts are subjected to ahigh temperature, and some cracks occur thereto, this will not lead todisintegration, causing no problem with reduction.

The facility for producing reduced iron according to the invention (theinvention described hereinbefore in (2) above) is the facility forcarrying out the invention described hereinbefore in (1) above.

The facility comprises a mixer for mixing the fine iron oxides with thepowdery solid reductants, a compactor for compacting the raw materialmixture obtained through the mixing step into the sheet-like compacts, afeeder for placing the sheet-like compacts on the hearth of thereduction furnace, and a rotary hearth furnace for reducing the ironoxides contained in the sheet-like compacts fed therein. The rotaryhearth furnace is provided with a furnace body having a feeding inletfor the sheet-like compacts, a discharge outlet for the reduced ironproduced through high temperature reduction of the iron oxides, and anexhaust outlet for off-gas generated therein, the hearth which isinstalled therein so as to be horizontally rotatable, and burners forcombusting the fuel after the fuel and the oxygen-containing gas areblown in.

FIGS. 4 and 5, and FIG. 2 shown hereinbefore are views for illustratingthe facility for producing reduced iron according to the invention. FIG.4 is a schematic illustration showing a production facility in itsentirety and an entire process. In the figure, the facility according tothe invention is shown in an area surrounded by a broken line. FIG. 5 isa vertical section of the rotary hearth furnace, showing a sectioncrossing the direction of movement of the hearth. FIG. 2 is a verticalsection of an example of a compacting and feeding apparatus, showing asection in parallel with the direction of movement of the rotary hearth.

As shown in FIG. 4, the facility for producing reduced iron according tothe invention comprises a mixer 22 for mixing the fine iron oxides withthe powdery solid reductants, a compacting and feeding apparatus notshown (disposed above the rotary furnace 11 as shown in FIG. 2) and arotary hearth furnace 11. The rotary hearth furnace is provided with afeeding inlet 23 for charging the mixture of raw materials (refer toFIG. 2), a discharge outlet 24 for reduced iron, and an exhaust outlet15 for gases generated therein (off-gas), and burners 25 for combustingfuel after the fuel and oxygen-containing gas are blown in.

In the figure, binders 29 and dust 30 in addition to fine iron oxides(fine iron ore) 27 and powdery solid reductants 28 are sent from hoppers26 for receiving raw materials to a mixer 22 for mixing. A part ofoff-gas 31 from a smelting furnace, used for generation of electricpower, and the like, is used as fuel for the method. Air 33 preheated byheat generated through combustion of gases (off-gas) exhausted from anexhaust outlet 15 in an off-gas combustion apparatus 32 is used for theoxygen-containing gas. The off-gas is discharged to atmosphere via adust collector 35 and a desulfurization apparatus 36 after passingthrough a heat exchanger 34. Reference numeral 37,38 denotes a blower.

As shown in FIG. 5, the hull of the rotary hearth furnace is a furnacebody 39, inside which a hearth horizontally rotatable (rotary hearth 13)is installed. A track 40 is attached to the underside of the hearth 13,and the hearth 13 is rotated at a predetermined speed by fixed drivingwheels 41 by a driving means 42. The furnace is sealed by sealing water43. The sheet-like compacts 18 placed on the hearth 13 are reduced byheat of combustion of the fuel blown in through the burner 25.

The compacting and feeding apparatus shown in FIG. 2 is constructed suchthat the mixture of raw materials 16 is compacted into the sheet-likecompacts 18 by rollers 17, and the sheet-like compacts 18 arecontinuously fed onto the hearth in step with advance of a platform carconstituting the rotary hearth 13. Reference numeral 19 denotes a shieldplate for protecting the roller 17 and the like from heat radiated fromthe hearth, and reference numeral 20 supporting rollers.

A variety of methods and apparatuses are available for charging themixture of raw materials into the rotary hearth furnace as describedmore specifically hereinafter.

For example, a method may be adopted wherein the mixture of rawmaterials is compacted into sheet-like shape, when charging same intothe reduction furnace provided with the rotary hearth, by use of adouble-roll compactor disposed above the hearth such that axes of thedouble rolls intersect the direction of advance of the hearth at rightangles, the sheet-like compacts discharged from the double-rollcompactor are received by a feeder chute, and then placed on the hearthfor production of reduced iron.

A reason for compacting the mixture of raw materials by the double rollcompactor disposed above the hearth such that the axes of the doublerolls intersect the direction of advance of the hearth at right anglesis to minimize handling from compacting until charging of feeds onto thehearth. That is, by adoption of a feeding method whereby compacted rawmaterial is once received by the feeding chute, and then placed on therotary hearth, material handling is limited to discharge of thecompacted raw material from the nip of the rolls of the double-rollcompactor onto the feeding chute and causing same to slide down alongthe chute onto the hearth, lightening impact on the compacted rawmaterial due to handling.

Then, a reason for compacting the mixture of raw materials by the doubleroll compactor provided with two rolls, the axes thereof intersectingthe direction of advance of the hearth at right angles is to charge thecompacted raw material discharged from the nip of the rolls of thedouble-roll compactor onto the hearth so as to slide down along thefeeding chute with little shift in the crosswise direction of thehearth. Consequently, the sheet-like compacts can be charged into thefurnace without cracking or the like occurring thereto.

FIG. 6 is a schematic illustration showing, by way of example, theprincipal mechanism of a feeding apparatus used in carrying out theinvention for feeding raw material for production of reduced iron. Asshown in the figure, the feeding apparatus is provided with thedouble-roll compactor 10 for compacting the mixture of raw materialssupplied from a raw material hopper 48, disposed above the rotary hearth13 (directly overhead in this case) such that the axes 46,47 of tworolls 44,45 intersect the direction of advance of the rotary hearth 13at right angles, and a feeder chute 49 for receiving and placing thesheet-like compacts 18 discharged from the double roll compactor 10 onthe rotary furnace.

The double roll compactor 10 has two rolls consisting of a pressing roll44 provided with a pressing roll gear 50, and a stationary roll 45provided with a stationary roll gear 51 which are disposed such that theaxis of the stationary roll 47 is fixed while the axis of the pressingroll 46 is movable in the direction of the arrow shown in the figure, orin the reverse direction for adjustment of pressure applied forcompacting the mixture of raw materials.

The pressure applied is to be adjusted depending on the kind of rawmaterial, the shape of the compacts, an amount of the binder, and like,however, may be unnecessary in a condition where compacting is achievedwith ease. Normally, the axes of the two rolls are disposed at the samelevel, however, may be at different levels.

As shown in the figure, the feeder chute 49 disposed immediately belowthe double roll compactor 10 is a chute inclined towards the directionof advance of the rotary hearth 13 so that the sheet-like compacts 18discharged from the nip of the rolls of the double roll compactor areplaced on the rotary hearth 13 with impact on the sheet-like compacts 18being softened.

In an embodiment shown in the figure, the pressing roll 44 is disposedon the side towards the direction of advance of the hearth 13 (that is,on the downstream side). Such positioning enables the sheet-likecompacts 18 to be subjected to less impact force and is thereforepreferable because larger compressive force acts on the sheet-likecompacts 18 on the side of the pressing roll 44 than on the side of thestationary roll 45, resulting in discharge of the sheet-like compacts ina condition slightly warped towards the side of the pressing roll 44.

Accordingly, by use of the feeding apparatus described above, thesheet-like compacts are subjected to less impact force until chargedonto the rotary hearth, and can therefore be placed thereon withoutcausing large cracks, and the like.

Alternatively, a plurality of double roll compactors provided with rollsshorter in length may be disposed in the transverse direction of therotary hearth to carry out the invention.

For compacting the mixture of raw materials by use of a single doubleroll compactor, a compactor provided with rolls having a lengthequivalent to a width of the rotary hearth is required, and furthermore,pressure at the center of each of the rolls becomes lower, reducingphysical strength of compacts. With use of the plurality of the doubleroll compactors provided with rolls short in length, but equivalent tothe width of the rotary hearth in total length, compacted raw materialof sufficient strength across the width of the hearth and with nodifference in strength along the longitudinal direction of the rolls canbe produced. As shown in FIG. 7, the plurality of the double rollcompactors are disposed in a staggered manner across the width of thehearth 13, not in alignment with each other, so that the sheet-likecompacts 18 discharged from the respective double roll compactors 10 areplaced on the hearth without gaps in-between.

A double roll compactor provided with tapered rolls, the diameter ofeach increasing towards the external circumference of the hearth, mayalso be used.

Since a transfer speed of the hearth is greater on the side of theexternal circumference than on the side of the internal circumference, afeeding rate of raw material per unit surface area of the hearth on theside of the external circumference differs from same on the side of theinternal circumference provided that a feeding rate of the sheet-likecompacts discharged from the double roll compactor remain constantacross the width of the hearth. As a result, in the case of a differencein the radius between the external circumference and the internalcircumference being large, or the hearth rotating at a high speed, thesheet-like compacts are subjected to stress when placed on the hearth,causing cracks or the like. In such a case, with use of the double rollcompactor provided with tapered rolls as described above, the feedingrate of the sheet-like compacts can be varied across the width of thehearth so that the feeding rate of raw material per unit surface area ofthe hearth is rendered unchanged from the external circumferential sideto the internal circumferential side.

A feeder chute having a part concavely curved in a longitudinal sectionalong the direction of advance of the furnace may be used in place ofthe flat plate type chute.

In the case of such a curved chute, it is desirable to use a chutehaving a tip tilted at a small angle, that is, in a conditionsubstantially horizontal so that a difference in height between the tipand the hearth is as small as possible. By charging the sheet-likecompacts through the feeding apparatus having the curved chute, verticalimpact force acting on the sheet-like compacts when placing same on thehearth is diminished, minimizing a risk of cracks, and the likeoccurring.

Further, a tip chute detachable, and attached rotatably around aconnection point as a fulcrum, and having the extremity thereof incontact with the hearth may be used in place of the feeder chute fixedlyattached to the feeding apparatus as described above.

When charging the sheet-like compacts along the feeder chute onto thehearth, it is desirable to minimize vertical impact force acting on thesheet-like compacts being charged by keeping the tip of the feeder chutein contact with the hearth. In the case where there have occurredasperities on the surface of the hearth, caused by adhesion thereto ofraw material, charging operation by use of the feeder chute fixed to thefeeding apparatus with the tip of the feeder chute, kept in contact withthe surface of the rotary hearth, the tip of the feeder chute can getcaught by the surface of the hearth, causing troubles, for example,deformation of the feeder chute.

Such a problem can be overcome by charging the sheet-like compacts usingthe feeding apparatus provided with the tip chute attached rotatablyaround a connection point as a fulcrum because the tip of the feederchute can make vertical movements, up and down, with ease according tothe asperities on the surface of the hearth, and is kept in constantcontact with the hearth without being caught by the asperities thereon.

A tip portion of the feeder chute in contact with the hearth wears out,and a length of the tip portion becomes shorter with progress in wearoutwith the result that the tip portion tends to tilt at a greater angleagainst the horizontal. In such a case, the tip portion can be simplyreplaced, making maintenance work much easier than for the case of thefeeder chute fixed to the feeding apparatus.

Production of reduced iron may be carried out by use of the double-rollcompactor disposed above the rotary hearth and provided with two rollssuch that the axes of the rolls intersect the direction of advance ofthe rotary hearth at right angles, when charging the mixture of rawmaterials into the reduction furnace provided with the rotary hearth sothat the mixture of raw materials is compacted into the sheet-likecompacts via a thin film in intimate contact with either one of therolls, and the sheet-like compacts are placed on the hearth togetherwith the film.

As the mixture of raw materials in a condition bonded to (pasted on) thefilm is discharged in a sheet-like form from the double-roll compactor,the sheet-like compact together with the film can be bent in thedirection of advance of the hearth (that is, in such a way as to cause ahorizontal angle of the tip of the sheet-like compact against the hearthto become small), and placed on the furnace for heating.

FIG. 8 (a) is a sectional view showing a schematic illustration of theconstruction of the feeding apparatus according to an embodiment of theinvention.

As shown in the figure, the apparatus comprises a film holder 54 forsupplying the film 53 to be passed in intimate contact with either one(stationary roll 45, in this case) of the rolls together with themixture of raw material through the double roll compactor, and rollers55 for supporting the sheet-like compact 18 in a condition substantiallypasted on the film, discharged from the double roll compactor, and forcausing the sheet-like compact 18 to be bent in the direction of advanceof the hearth 13. In the case of this embodiment, the feeding apparatusis provided with a guide chute 56 for guiding the sheet-like compact 18transferred by the rollers 5 for supporting the sheet-like compact ontothe hearth.

For the film to be passed together with the mixture of raw materialsthrough the double roll compactor, a material which is wide, long, thinin a film-like shape, and in addition, combustible in the rotary hearthfurnace is required. Inorganic constituents contained in the film willremain in reduced iron products. Accordingly, a hydrocarbon-based orcarbohydrate-based film containing hardly any inorganic constituents ispreferable. More specifically, polyethylene or paper describedhereinafter is a suitable material.

In the method and the apparatus therefor according to the invention, themixture of raw materials is compacted via the thin film, the sheet-likecompact obtained is unsusceptible to cracking and the like, and thesheet-like compact wide in width can be placed on the hearth with ease.

Production of reduced iron may also be carried out by use of thedouble-roll compactor, when charging the mixture of raw materials intothe reduction furnace provided with the rotary hearth, wherein themixture of raw materials is compacted into the sheet-like compacts via abelt in intimate contact with either one of the rolls, the sheet-likecompact is transferred together with the belt to a position in closeproximity of the hearth, and then, the raw material sheet is separatedfrom the belt so that the raw material sheet is placed on the hearthwhile the belt is returned to the double roll compactor.

FIG. 8 (b) is a sectional view showing a schematic illustration of theconstruction of the feeding apparatus according to another embodiment ofthe invention.

As shown in the figure, the apparatus comprises sheet-supporting rollers55 for supporting an endless belt 57, to be passed in intimate contactwith either one (stationary roll 45, in this case) of the rolls togetherwith the mixture of raw material through the double roll compactor, andfor supporting the sheet-like compact 18 in a condition substantiallypasted on the belt, discharged from the double roll compactor, as wellas for causing the sheet-like compact 18 to be bent in the direction ofadvance of the hearth 13, and belt carrier rollers 58 for driving thebelt. In the case of this embodiment, the feeding apparatus is providedwith a guide chute 56 for guiding the sheet-like compact 18 transferredby the sheet-supporting rollers onto the hearth. The guide chute may bein a plate-like form, however, a roller chute is preferable for smoothflow of the raw material sheet.

For the belt to be passed together with the mixture of raw materialsthrough the double roll compactor, a material needs to be wide and long.And, strength sufficient for continuous use is required. Morespecifically, a belt made of rubber can be used, however, a metallicbelt described hereinafter is preferable.

The sheet-like compact obtained by use of the apparatus is unsusceptibleto cracking, and the sheet-like compact wide in width can be placed onthe hearth with ease while the belt for holding compacted raw materialin a sheet-like form can be circulated endlessly. Further, since onlythe sheet-like compact is loaded on the hearth, there is not risk ofimpurities being mixed into reduced iron products.

Production of reduced iron may further be carried out by use of a methodwherein in charging the mixture of raw materials into the reductionfurnace provided with the rotary hearth, the mixture of raw materials issupplied onto a tilted chute constituted by a belt circulating in thedirection of advance of the hearth, disposed above the hearth, andcompacted into sheet-like shape by a roller so that the sheet-likecompact on the belt, after transferred to a position in close proximityof the hearth, is separated from the belt for further transfer onto afeeder chute in flat plate form, and then placed on the hearth.

In this instance, the sheet-like compact can be placed on the hearthmore smoothly by causing a supplementary transfer belt constituted by abelt circulating in the direction of advance of the hearth to be incontact with the surface of the sheet-like compact so as to place thesheet-like compact on the hearth by the agency of driving force of thebelt.

FIG. 9 is a schematic illustration showing the construction of anapparatus for carrying out the method according to a further embodimentof the invention as described above.

As shown in FIG. 9, the apparatus comprises rollers 59 for compactingthe mixture of raw materials 16 fed from a raw material hopper 48 intothe sheet-like compact, a tilted chute 60 for receiving the mixture ofraw materials 16 from the raw material hopper 48 and transferring samein the direction of advance of the hearth 13, and a feeder chute 62 inflat plate form for receiving the sheet-like compact formed on the belt61 by compressive force of the rollers 59 composing the tilted chute 60and transferred together with the belt to a position in close proximityof the hearth. The rollers 59 are disposed so as to compress the mixtureof raw material 16 on the tilted chute 60. It is desirable to squeezethe belt 61 of the tilted chute 60 therebetween from both sides, inorder to compress the mixture of raw material strongly.

The mixture of raw materials 16 released from the raw material hopper 48is supplied onto the tilted chute 60 to a predetermined thickness bymeans of the supply regulator plate 66, compacted on the tilted chute 60into a sheet-like shape by the rollers 59, and transferred towards thedirection of advance of the hearth 13.

Further, the apparatus is provided with a supplementary transfer belt 63constituted by a belt 64 moving in the direction of advance of thehearth 13, disposed so as to be in contact with the surface of thesheet-like compact 18. The sheet-like compact is pushed towards thedirection of advance of the hearth by driving force of the belt 64, andplaced on the hearth more smoothly. A supplementary transfer belt may bedisposed in the feeding apparatus shown in FIG. 6.

The roller, the tilted chute and the feeder chute may be divided into aplurality of rollers, tilted shutes and feeder shutes.

Production of reduced iron may further be carried out by use of a methodwherein in mixing fine iron oxides with powdery solid reductants, all offine iron oxides, powdery solid reductants, water, and a binder to beadded as necessary are fed together into a mixer incorporatinghigh-speed agitation impellers rotating at not less than 300 rpm,adjusting mixing so that a proportion of water to all raw materialsbecomes 6 to 18 mass %, and a mixture obtained is compacted into asheet-like shape, and charged into the reduction furnace provided withthe rotary hearth.

That is, for production of compacts having high strength by improvingviscosity of fine raw material, hard mixing using a high-speed agitationmixer is applied to attain higher strength. In balling and compacting ofpowders in moist condition, wetting between powder particles occurs bywater and liquid binders, and resultant capillarity causes aggregationforce to act between the powder particles, achieving balling andcompacting as well as higher strength. Hence, it is effective to applyhard mixing with strong agitation force to facilitate intrusion of waterand binders between the powder particles.

To obtain the effect described above, it is effective to apply agitationmixing by use of the high-speed agitation mixer at not less than 300 rpmof revolution rate of the agitation impellers (that is, revolution rateof the high speed agitation mixer). This is because fine raw material isseparated in unit of each particle at not less than 300 rpm ofrevolution rate of the high speed agitation mixer, and water and bindersare more uniformly diffused between particles, effectively contributingto enhancement in strength while at less than 300 rpm of the revolutionrate, separation in unit of each particle does not occur with no effecton strength.

A binder need not be added, however, is quite effective in enhancingstrength because as described in the foregoing, in balling andcompacting of powders in moist condition, the binder acts to enhance thestrength of compacts in the same way as water, and even more intenselythan water. Further, since hard mixing is applied, less amount ofaddition is required than in the case of mixing by use of an ordinarymixer, for example, an edge runner mill, or the like, thus contributingto restraining an increase in production cost and deterioration in thequality of reduced iron due to addition of the binder. Accordingly, itis effective to add a binder if need be taking into account the kind,and the like of raw material used. Tar, theriac, bentonite, and the likecan be used for a binder, and an adequate amount of a binder to be addedmay be decided upon according to the kind of a binder to be used.

The reason for charging all of fine iron oxides, powdery solidreductants, water, and a binder to be added as necessary together intothe high-speed agitation mixer is to obtain raw materials effectivelymixed in a short time.

In this instance, water is added in such an amount that water content inthe whole raw materials becomes 6 to 18% by mass. This is because incase of water exceeding 18% by mass, the effect of high speed agitationwhereby water is uniformly diffused between powder particles can not beachieved owing to presence of excess water, while in case of water beingless than 6% by mass, the effect of high speed agitation is limitedowing to presence of irregularity in uniform diffusion of water betweenthe powder particles due to lack of water. Water added may be in theform of not only liquid water but also vapor. Vapor having higherdiffusibility is more effective than water.

Production of reduced iron may be carried out by a method wherein fineiron oxides containing 4.0 to 10.0% by mass of Al₂ O₃ and SiO₂ in totalare used for mixing with powdery solid reductants.

Al₂ O₃ and SiO₂ are main constituents composing clay content, and thehigher the content of Al₂ O₃ and SiO₂ in raw material, that is, the claycontent, the higher the strength of compacts formed therefrom. The claycontent contained in fine iron oxides has better diffusibility than thatof adhesive constituent in binders, and is able to provide sufficientadhesive force to each particle composing fine iron oxides.

In this method, the strength of compacted raw material is enhanced bymaking full use of the clay content contained in fine iron oxidesinstead of making use of adhesive force of binders as in the case ofconventional methods.

The content of Al₂ O₃ and SiO₂ in total is set in the range between 4.0to 10% by mass because at less than 4% by mass, the effect of enhancingthe strength of compacts is insignificant due to insufficiency in theclay content while in excess of 10% by mass, excessive clay content isincluded in reduced iron, degrading product quality.

In carrying out the method according to the invention, a binder may beadded to a mixture of fine iron oxides and powdery solid reductants.Addition of the binder does not lead to diminishment in the effect ofthe method according to the invention with no adverse effect whatsoever.

Production of reduced iron may be carried out by a method wherein inmixing fine iron oxides with powdery solid reductants, fine iron oxidescontaining not less than 80% by mass of fines less than 0.1 mm in size,and coal, as powdery solid reductants, containing not less than 6% bymass of moisture, and not less than 50% by mass of coal fines not lessthan 0.1 mm and not more than 1 mm in diameter are used.

Use of fine iron oxides in small size, and use of coal in larger size assolid reductant are due to the fact that fine iron oxides are of highdensity while coal becomes very porous as volatile constituents isreleased when heated up to 500° C., and highly reactive even though inlarge size.

The reason for selecting the coal containing not less than 6% by mass ofwater and not less than 50% by mass of particles not less than 0.1 mmand not more than 1 mm in particle diameter is that coal stored in acoal yard normally contains not less than 6% by mass of water, and sizedistribution of the coal after crushing without drying is not less than50% by mass of particles not less than 0.1 mm and not more than 1 mm inparticle diameter. The upper limit of water in coal is an amount whichcan be absorbed during storage in the coal yard, and there is nospecific numerical limitation. Against coal under such condition, fineiron oxides in adequate size are those containing not less than 80% bymass of fines-0.1 mm (passing through 0.1 mm sieve) in size.

In carrying out this method, there are cases where recovery rate of coalin size between 0.1 mm and 1 mm declines because when crushing coalmeeting the condition described above, adhesion of a portion of coal toa crusher can occur.

Such adhesion of coal to the crusher is effectively prevented by use ofa method whereby coal is crushed in admixture with a portion of ironore. Soft material such as coal is prone to adhesion, but hard materialsuch as iron ore is not. Hence, adhesion can be restrained by crushingmixture of both materials. Iron ore to be mixed with coal when crushingthe coal need not contain not less than 80% by mass of fines-0.1 mm insize, and iron ore of coarse particle size may be used for the purpose.

In this method, a crusher used for adjusting sizes of fine iron oxidesand/or powdery solid reductants is not limited to any particular type.Any type of crusher such as impact mill, roller mill, rod mill, ballmill, and the like may be used.

In carrying out this method, a binder may be added to a mixture of fineiron oxides and powdery solid reductants. Addition of the binder doesnot lead to diminishment in the effect of the method with no adverseeffect whatsoever.

Further, with this method, gaps among particles of raw material makingup the sheet-like compact, that is, porosity can be reduced and densefilling is achieved, enhancing the strength of the sheet-like compactcharged into the rotary hearth furnace, and reducibility of fine ironoxides. As a result, reduced iron of high metallization ratio can beproduced.

In a conventional method of producing reduced iron, agglomerates(pellets) are laid on the hearth to a thin thickness of 10 to 20 mminside a rotary hearth furnace inside which temperature is maintained inthe range of 1100 to 1300° C., the temperature of the agglomerates risesto not less than 900° C. mainly by heat radiated from the inner wall ofthe furnace, the agglomerates are reduced and sintered while adjusting arotation speed of the hearth such that a predetermined metallizationratio is reached every time the hearth completes one turn, and productsare discharged from a discharge outlet by a screw feeder.

FIG. 10 is a schematic illustration of a method of discharging reducediron by the screw feeder used for discharging refuse, FIG. 10 (a) a topview of the rotary hearth, and FIG. 10 (b) a longitudinal sectional viewof the vicinity of the discharge outlet. As shown in the figure, whilemixture of raw material 16 charged onto the rotary hearth 13 from afeeding inlet 12 makes one turn accompanying a rotation of the hearth,iron oxides in the raw material are reduced at a high temperature, anddischarged as reduced iron from the product discharge outlet 14 by thescrew feeder 67. Reduced iron, after reaching the screw feeder 67, istransferred in the direction (as shown in the figure by the arrows inblank) at right angles against the direction of advance of the hearth 13by rotation of the screw feeder, and discharged towards the peripheralside of the hearth 13. Further, immediately behind the screw feeder 67,a stopper fence 68 for storing reduced iron is installed. In the exampleas shown, a track 40 is provided under the hearth 13, and the hearth 13is rotated at a predetermined speed by fixed driving wheels 41. Theinside of the furnace is sealed by sealing water 43.

Transfer of reduced iron by the screw feeder is at a very slow speed,however, taking a fairly long time until reduced iron is dischargedafter reaching the peripheral side of the hearth. Consequently, quantityof reduced iron residing in front of the screw feeder increases.Particularly, reduced iron located on the edge of the hearth, on theside of the inner circumference thereof, ends up staving in the furnacefor a long time because it needs to be transferred for a distance fromthe inner circumference side to the external circumference side, andfurther, is mixed up with reduced iron placed at other parts of thehearth.

To overcome such a problem, reduced iron produced by firing in therotary hearth furnace needs to be discharged from the furnace rapidly.To this end, a number of methods described hereinafter may be adopted.

Production of reduced iron may be carried out by use of a method wherebyreduced iron produced through reduction of iron oxides in the reductionfurnace having the rotary hearth is discharged by, for example, apushout device reciprocatingly movable in the direction at right anglesto the direction of advance of the hearth.

FIGS. 11 (a) and 11 (b) are views illustrating an example of the methodusing a pusher as the pushout device. FIG. 11 (a) a schematic plan view,and FIG. 11 (b) is a cross-sectional view of FIG. 11 (a) at sectionA--A. As shown in the figures, the pusher 69, in plate form, serving asthe pushout device, and reciprocally movable in the direction at rightangles to the direction of advance of the hearth is disposed on the sideof the inner circumference of the hearth (outside the hearth) in adischarge area of the rotary hearth furnace.

Reduced iron advancing towards the discharge area accompanying rotationof the hearth 13 is pushed out of the peripheral side of the hearth bymovement of the pusher 69 in the direction of the arrow, and dischargedvia a discharge chute 70. In the example shown in the figure, as astopper fence 68 is provided on the downstream side (on the side towardsthe direction of advance of the hearth) of a range of movement of thepusher 69 as shown by broken lines, and the pusher 69 moves along thestopper fence 68, discharge of entire reduced iron without any leftoveris ensured. The pusher 69, after reaching the peripheral edge of thehearth, returns to its original position, and moves in the direction ofthe arrow for next discharge operation.

Production of reduced iron may be carried out by a method wherebyreduced iron is discharged towards both sides of the hearth along adischarge guide fence provided on the hearth, and formed in the shaperesembling the letter V based at the center across the hearth, andspread in the direction of advance of the hearth instead of the methodby the pushout device described above.

FIGS. 11 (c) and (d) are views illustrating an example of the method.FIGS. 11 (c) a schematic plan view, and FIGS. 11 (d) is across-sectional view of FIGS. 11 (c) at section B--B. As shown in thefigures, a discharge guide fence 71 formed in the shape resembling theletter V, based at the center of the hearth 13 crosswise, and spreadingin the direction of advance of the hearth 13 (towards downstream), isprovided on the hearth, the spread on respective sides of V forming anangle of 45° with the direction of advance of the hearth.

When reduced iron transferred to the discharge area accompanyingrotation of the hearth 13 reaches the discharge guide fence 71, reducediron is split along the discharge guide fence 71 to the right and theleft, and guided to discharge chutes 70 provided on both sides. In theexample shown in the figure, supplementary guide fences 72 are providedbefore the discharge guide fence and in parallel therewith to smooth outdischarge flow so that reduced iron 73 is discharged without stagnation.

There is no particular restriction on the angle at which the dischargeguide fence is installed, however, from the viewpoint of dischargingreduced iron rapidly out of the furnace without stagnation of reducediron on the hearth, it is desirable to install the discharge guide fenceto form 45° with the direction of advance of the hearth on respectivesides thereof.

The discharge guide fence having a sufficient height so as not to permitreduced iron reaching the discharge area to go over before guided to thedischarge chutes may be used.

With the method, reduced iron produced by firing in the rotary hearthfurnace can be discharged rapidly out of the furnace, preventing adecline in metallization ratio due to reoxidation of reduced iron asdescribed hereinbefore, and avoiding a decrease in heating area on thehearth resulting from installation of a cooling apparatus to preventreoxidation so that productivity of reduced iron can be maintained.

In the conventional processes of producing reduced iron described in theforegoing, when charging agglomerates (pellets) into the rotary hearthfurnace, powdering occurs to the agglomerates, generating fines. Evenafter charging, cracking occurs during reduction at a high temperature,generating fines. Fines thus generated are reduced into metallized ironpowders (reduced iron fines) in the rotary hearth furnace. The reducediron fines penetrate through gaps between the stopper fence installed inthe discharge area and the hearth, stay on the hearth without beingdischarged, recycled to the feed inlet accompanying rotation of thehearth, and subjected to heating. Thus the reduced iron fines arecirculated repeatedly, and stay on in the furnace.

The reduced iron fines staying in the furnace remain in powdery form fora while, however, after a length of time, reduced iron fines aresintered with each other, and stick to the hearth as adhesive matter.Before long, the hearth will be in a condition as if coated by a steelplate, and asperities are caused to occur on the surface of the hearthdue to thermal deformation. With such asperities occurring on thesurface of the hearth, irregularities in firing results when firing rawmaterial with the result that not only deterioration in metallizationratio of reduced iron but also operational trouble may occur, posing arisk of major operational problems. Furthermore, iron adhered to thehearth bricks creates a cause for breakage of the bricks due toexfoliation when mechanical force is applied thereto.

In the method of producing reduced iron according to the invention, asthe mixture of raw materials is charged into the reduction furnace aftercompacted into a sheet-like shape, generation of fines is far less thanin the conventional method wherein raw material in the form ofagglomerates is charged into the reduction furnace. Still, generation offines is unavoidable as cracking occurs in the course of reduction at ahigh temperature. Hence, countermeasures to cope with the problemdescribed above are required to maintain stable operation for a longtime.

A method of removing reduced iron fines remaining on the hearth byblowing off with injected gas flow between the reduced iron dischargearea and the raw material feeding inlet may be used as a countermeasure."Between the reduced iron discharge area and the raw material feedinginlet" refers to an interval on the hearth from the reduced irondischarge area to the raw material feeding inlet along the direction ofadvance of the hearth, where neither raw material nor reduced ironproduced therefrom is placed on.

FIG. 12 is a schematic illustration showing an example of the method.The figure show a section crossing the direction of advance of thehearth. As shown in the figure, a nozzle 74 for gas injection isdisposed in a manner tilted downward towards the surface of the hearth,and remaining reduced iron 75 is blown off by gas injected from thenozzle 74, keeping the surface of the hearth clean.

There is no restriction on an angle formed between the nozzle and thesurface of the hearth, and a height of the nozzle from surface of thehearth. Both may be adequately adjusted so as to blow off remainingreduced iron and effectively remove same from the surface of the hearth.

Gas may be injected towards the direction of advance of the hearth fromthe nozzles disposed side by side along the direction at right angles tothe direction of advance of the hearth, however, it is desirable toinject gas towards the direction at right angles to the direction ofadvance of the hearth, or the direction substantially similar theretofrom reciprocatingly movable nozzles by moving same as shown by thearrow in the figure.

In the case that the nozzle for gas injection is circular orsubstantially circular in section at the tip thereof, a plurality of thenozzles, instead of a single nozzle, may preferably be disposed inparallel around the periphery of the hearth. Nozzles flat and spreadingin the direction of the circumference of the hearth in section at thetip thereof may also be used.

There is no particular restriction on the kind of gas injected, however,from the viewpoint of protection of the hearth bricks and prevention ofreoxidation of remaining reduced iron fines, nitrogen gas is preferable.

Further, there is no restriction on injection pressure of gas, and theinjection pressure may be adequately adjusted so as to be able to removereduced iron from the hearth effectively.

Production of reduced iron may be carried out by use of a method ofremoving reduced iron remaining on the hearth by sweeping same outbetween the reduced iron discharge area and the raw material feedinginlet with brooms provided with a rotatable feather. In this context,"broom provided with a rotatable feather" refers to a device capable ofsweeping out reduced iron remaining on the hearth, and is not limited toa broom having a feather or feather-like object. A broom provided with ahair-like object of a predetermined hardness and thickness (so calledbrush) or the equivalent may be used.

For example, a cylindrical broom surrounded by a cleaning brush androtatable in one direction and reverse direction around the axis thereof(that is, rotatably reciprocating) may be used for the broom providedwith the rotatable feather. The broom 76 provided with the rotatablecleaning brush as shown in an enlarged view of FIG. 13 corresponds tothe aforesaid broom.

The remaining reduced iron is removed from the surface of the hearth bysweeping same out with such type of the broom provided with therotatable feather, the broom being rotated in one direction or reversedirection as appropriate while reciprocatingly moved in the direction atright angles or substantially at right angles to the direction ofadvance of the hearth.

FIG. 13 is a schematic illustration of the method according to anpreferred embodiment of the invention, showing a vertical sectional viewagainst the direction of advance of the hearth.

In this embodiment, for the broom provided with the rotatable feather,use is made of a plurality of groups 79 composed of cylindrical brooms76 (refer to the enlarged view) provided with a cleaning brush 77attached to the peripheral surface thereof and rotatable in onedirection and reverse direction around the axis 78 thereof, which aregrouped in annular fashion on a plane normal to the axis of thecylindrical broom 76. More specifically, a plurality (two in the figure)of groups 79 of the brooms 76 provided with the rotatable cleaning brushare disposed between the reduced iron discharge area and the rawmaterial feeding inlet across the hearth 13, and the reduced ironremaining on the hearth is removed by rotating respective brooms 76provided with the rotatable cleaning brush, composing each group 79, inone direction or reverse direction as appropriate while rotating eachgroup 79 itself in annular ring in one direction or reverse direction atright angles or substantially at right angles to the direction ofadvance of the hearth. A group 79 in annular ring of the brooms 76 maybe disposed on the hearth, and reciprocatingly moved in the directioncrossing at right angles or substantially at right angles to thedirection of advance of the hearth while being rotated as describedabove.

By use of the groups of the brooms provided with the rotatable cleaningbrush, each in annular ring formation, the remaining reduced iron finescan be effectively removed in short time, keeping the surface of thehearth clean.

There is no particular restriction on the width of the brooms providedwith the rotatable feather, however, the width same as that of therotary hearth is preferable.

There is no particular restriction on a transfer speed of the broomprovided with the rotatable feather, however, a speed same as or higherthan that of the hearth is required provided that the entire surface ofthe hearth is to be cleaned by the brooms provided with the rotatablefeather, having the width same as that of the hearth

In case that reduced iron fines as well as adhesive matter remain on thehearth, production of reduced iron may preferably carried out by use ofa method whereby the reduced iron fines and adhesive matter are removedby scraping same off with a scraper reciprocally movable in thedirection crossing the direction of advance of the hearth between thereduced iron discharge area and the raw material feeding inlet, andhaving the lower edge kept in touch with the hearth.

FIG. 14 is a schematic illustration of the method according to anembodiment of the invention, showing a vertical sectional view againstthe direction of advance of the hearth. As shown in the figure, thescraper 80 is disposed such that the lower edge thereof is kept in touchwith the surface of the hearth and the scraper can make reciprocalmovement in the direction crossing the direction of advance of thehearth 13. In this context, the direction crossing the direction ofadvance of the hearth refers to the direction intersecting the directionof advance of the hearth at right angles or substantially at rightangles (direction forming plus 20° or less to the direction intersectingthe direction of advance of the hearth at right angles or minus 20° orgreater to same).

In the method, reduced iron fines and adhesive matter remaining on thehearth are scraped off and removed from the surface of the hearth byreciprocally moving the scraper in the direction crossing the directionof advance of the hearth. From the viewpoint of shortening a distance ofmovement, reciprocal movement in the direction at right angles to thedirection of advance of the hearth may be preferable. As shown in thefigure, the scraper with the end thereof tilted at an appropriate angleis effective in scraping off foreign matter, and can remove adhesivematter adhered to the hearth. A width of the scraper, substantially sameas that of the hearth, is preferable.

Production of reduced iron may be carried out by use of a method wherebyreduced iron remaining on the hearth is removed from the surface of thehearth by sucking same in through a suction hood provided between thereduced iron discharge area and the raw material feeding inlet.

FIG. 15 is a schematic illustration showing a case of sucking in by useof a suction blower according to the method of the invention. The figureshows a vertical sectional view against the direction of advance of thehearth.

As shown in the figure, the suction hood 81(partitioned into sixcompartments in the figure) is provided over the hearth between thereduced iron discharge area and the raw material feeding inlet, and thepartitioned compartments are joined together into a single pipe andfinally connected with a suction blower 83 via a bag filter 82. Reducediron fines are sucked in by the suction blower 83 and recovered by thebag filter 82.

The suction hood may preferably be provided covering the whole width ofthe hearth.

In the case that reduced iron is discharged by the conventional typescrew feeder instead of the aforesaid pushout device or the dischargeguide fence in the shape of the letter V, use is preferably made of amethod whereby a scraper type gate with the lower end thereof kept incontact with the hearth is provided immediately behind (as seen in thedirection of advance of the hearth) the fixed stopper fence installed inthe reduced iron discharge area to prevent reduced iron fines fromremaining on the hearth.

FIG. 16 is a schematic illustration of the method according to anembodiment of the invention, showing a longitudinal sectional view inparallel with the direction (shown by the arrow in the figure) ofadvance of the hearth.

As shown in the figure, the scraper type gate 84 with the lower endthereof kept in contact with the hearth is provided in the direction ofadvance of the hearth of the fixed stopper fence 68 for storing reducediron products, installed behind (on the downstream side) the screwfeeder 67.

A small gap exists between the lower end of the fixed stopper fence 68and the surface of the hearth, and increases in size gradually due tofriction between reduced iron and the surface of the hearth duringdischarging of reduced iron. Consequently, reduced iron fines can passthrough the gap, remaining on the hearth without being discharged, andsubjected to heating after returning to the raw material feeding inletaccompanying rotation of the hearth. While such circulation is repeated,reduced iron fines stay on inside the rotary hearth furnace. To copewith this problem, the scraper type gate 84 is provided behind the fixedstopper fence 68. The scraper type 84 gate is disposed so as to belightly pressed down and kept in contact with the surface of the hearth13, closing the gap. Therefore, reduced iron fines passing through thegap between the fixed stopper fence 68 and the surface of the hearth areblocked by the scraper type gate 84, and reduced iron fines 75 areprevented from remaining on the hearth, maintaining the surface of thehearth clean.

The scraper type gate 84 may preferably be installed immediately behindthe fixed stopper fence 68, that is, in intimate contact with the fixedstopper fence 68 as shown in the figure provided that the scraper typegate can be kept lightly pressed down without any difficulty. Further,in case that the gap between the fixed stopper fence 68 and the surfaceof the hearth varies in height in the direction crossing the hearth, thescraper type gate is preferably divided across the width of the hearth.

With the method, the hearth can be kept clean by forestalling reducediron fines from remaining on the hearth.

The method of producing reduced iron according to the invention iscarried out with ease by use of the apparatuses according to theinvention hereinbefore described, fully demonstrating features of theinvention.

The method of producing hot metal according to the invention (theinvention under (3) and (4) above) is the method whereby hot metal isproduced using reduced iron in hot condition produced by the methodaccording to the invention under (1) above. The method (3) relates tothe case of using the shaft furnace, and the method (4) relates to thecase of using the in-bath smelting furnace.

The aforesaid methods are same as the invention (1) with respect to thesteps of mixing raw materials and reduction, that is, from the step a)to step d) in the invention (3) and (4) as described in DISCLOSURE OFTHE INVENTION, and various embodiments described above adopted by theinvention (1) may be used singly or in combination.

Accordingly, the steps from e) to g) are described hereinafter.

The step e) relates to a process of discharging reduced iron obtained bythe reduction step [referred to as pre-reduction step in the method ofproducing hot metal according to the invention (3) and (4)], at atemperature not less than 500° C., from the pre-reduction furnace.

The reason for setting the discharge temperature at not less than 500°C. is that at this temperature or higher, melting rate of reduced ironis increased by making full use of heat of reduced iron for thesucceeding step of melting, and energy efficiency for the whole processis improved while production facilities are economized. However, when atemperature inside the sheet-like compact is at not less than 1170° C.on discharge, there is a possibility of liquid melt being present insidethe sheet-like compact posing a risk of trouble in discharge operation.Hence, it is desirable to stop heating so that the temperature insidethe sheet-like compact declines below 1170° C. before discharging fromthe furnace. For a method of lowering the temperature inside thesheet-like compact below 1170° C. in short time, various methods such asa method of blowing a reducing gas at an ambient temperature, an inertgas, for example, nitrogen gas, and the like onto the surface of thesheet-like compact, a method of bringing a water-cooled plate in contactwith the surface of the sheet-like compact, or the equivalent may beused.

The next step f) relates to a process of reduction and melting. In themethod of producing hot metal according to the invention (3), the shaftfurnace is used.

FIG. 17 is a schematic illustration showing the steps of the method ofproducing hot metal according to the invention (3) and the apparatusesused for carrying out the method. As shown in the figure, reduced ironin hot condition is continuously discharged from the discharge outlet 24of the rotary hearth furnace 11, and sent out to the shaft furnace 85for the step of reduction and melting.

In the case that the shaft furnace is located at a distance, reducediron is transported in a closed container (not shown) with inert gassuch as nitrogen gas sealed therein. Normally, however, the shaftfurnace is installed adjacent to the rotary hearth furnace, which is apre-reduction furnace, and reduced iron is fed into the shaft furnace bya bucket conveyer or the like through an enclosed passage filled withinert gas such as nitrogen or reducing gas such as off-gas from theshaft furnace. Since reduced iron is sintered in the shape of a plateupon completion of pre-reduction, same may be transported by a conveyerafter light and rough crushing.

In the step of reduction and melting, reduced iron in hot condition,lumpy carbon material (coke, coal, and the like) 86, and flux 87 foradjusting basicity of slag are charged into the shaft furnace from thetop thereof, wherein a carbon material filled layer is laid, and areducing gas at a high temperature is generated through combustion ofthe carbon material placed in front of the tuyeres 88, through whichoxygen-containing gas (for example, air 89) or oxygen 90 is blown in.After reduction and melting, hot metal and slag 91 are discharged fromthe tap hole provided in the lower part of the furnace.

A furnace used for smelting in the method according to the invention isthe shaft furnace as above wherein a combustion zone in front of thetuyeres is surrounded by the carbon material as in the case of the blastfurnace, and consequently, breakage of refractory bricks due to exposureto high temperatures is prevented. Further, as opposed to the case ofthe method disclosed in Japanese Patent Publication No. H 3-60883wherein molten iron bath in the smelting furnace is agitated, the shaftfurnace used in the method is effective in lengthening the life ofrefractory bricks because there is no agitation in molten iron bathinside the shaft furnace.

Further, as reducing atmosphere in the shaft furnace wherein the carbonmaterial filled layer is formed is as strong as that in the case of theblast furnace, sulfur content in hot metal can held down low, producinghigh quality hot metal while concentration of FeO can be kept as low asin the case of the blast furnace, contributing to restraining depletionof refractory bricks.

In terms of thermal efficiency too, high thermal efficiency is ensuredby the method because counter-current heat transfer takes place betweengas and solids (charged raw material) in the shaft furnace, from the topof which carbon material and reduced iron are charged as in the case ofthe blast furnace. In the case of using cokes for carbon material, asshown in the figure, consumption of cokes may be reduced by blowing incarbon-bearing material 92 through the tuyeres 88, and blowing in air 89through the sidewall above the tuyeres so that heat generated bycombustion of CO gas and H₂ gas can be used for melting of reduced iron.

Dust generated from the shaft furnace may be used within the facility.

In the example shown in FIG. 17, dust 30 and the equivalent are blown inthrough the tuyeres 88 of the shaft furnace 85 while same is used in therotary hearth furnace 11 as a part of raw material. Such recyclingcontributes to improvement in utilization efficiency of raw material andfuel while waste disposal becomes unnecessary without emission of dust,and the like outside the facility, making the method advantageous fromthe standpoint of cost and environmental protection.

In the method of producing hot metal according to the invention (4)above, the in-bath smelting furnace is used in the step of reduction andmelting.

FIG. 18 is a schematic illustration showing the steps of the method ofproducing hot metal according to the invention (4) and the apparatusesused for carrying out the method. As shown in the figure, reduced iron73 in hot condition is continuously discharged from the discharge outlet24 of the rotary hearth furnace 11, and sent to the next step ofreduction and melting to be carried out in the in-bath smelting furnace94.

In the case that the in-bath smelting furnace is located at a distance,reduced iron is transported in a closed container with inert gas such asnitrogen as in the case of the shaft furnace. Normally, however, thein-bath smelting furnace is installed adjacent to the rotary hearthfurnace, which is a pre-reduction furnace, and reduced iron is fed intothe in-bath smelting furnace by a bucket conveyer or the like through anenclosed passage filled with inert gas such as nitrogen or reducing gassuch as off-gas from the in-bath smelting furnace. Since reduced iron issintered and in the shape of a plate upon completion of pre-reduction,same may be transported by a conveyer after light and rough crushing.

In the step of reduction and melting, reduced iron 73 in hot condition,carbon material 86, and flux 87 for adjusting basicity of slag arecharged into the in-bath smelting furnace 94 from the top thereof,wherein molten iron bath 95 and molten slag bath 96 are present and agas for agitation 97 is blown in from the bottom thereof for agitationof the molten iron bath and molten slag bath while oxygen is suppliedfrom the top side via a water cooled lance 98. After reduction andmelting, hot metal and slag 91 are discharged from the tap hole providedin the lower part of the furnace.

In the in-bath smelting furnace, reduced iron, ash content in carbonmaterial, and flux are melted by heat generated by combusting carbonmaterial charged into the furnace from the top thereof, and furthercombusting CO gas generated through reduction of unreduced iron oxidescontained in reduced iron and a portion of combustible gases issued fromcarbon material while the unreduced iron oxides contained in reducediron is reduced by the carbon material. The combustible gases issuedfrom the carbon material are CO gas, H₂ gas, and the like. In thisinstance, heat required for reduction of iron oxides, and also, carbonrequired for carburizing into the molten iron bath are supplied.

Generally, coal is used for carbon material, and burnt lime or dolomite,or the like are used for flux.

The in-bath smelting furnace is quite advantageous in that as cokes arenot used therein as opposed to the case of the blast furnace, hardcoking coal is not required with the result that it can do without cokeovens requiring huge capital outlay, and under operational constraintfrom environmental considerations.

Dust 30, and the like generated from the in-bath smelting furnace may beused within the facility. In the example shown in FIG. 18, generateddust is charged into the in-bath smelting furnace 94 from the top sidewhile being used for a part of raw material charged into the rotaryhearth furnace. Such recycling contributes to improvement in utilizationefficiency of raw material and fuel while waste disposal becomesunnecessary without emission of dust, and the like outside the facility,making the method advantageous from the standpoint of cost andenvironmental protection.

The step (g) relates to a process of gas recovery whereby gasesgenerated in the shaft furnace or the in-bath smelting furnace arerecovered while a portion of the gases is supplied to the pre-reductionfurnace as fuel for pre-reduction. More specifically, as shown in FIGS.17 and 18, generated gases (off-gas 31) are recovered after removal ofdust, and the like through a dust collector 93 such as cyclone or thelike. The recovered gases are sent to downstream steps or used for powergeneration.

Thus, in the method of producing hot metal according to the invention(3) or (4), redeced iron is produced through rapid reduction of ferrousraw material in fine form charged in the pre-reduction furnace, and highquality hot metal is produced by charging the reduced iron in hotcondition into the shaft furnace or the in-bath smelting furnace, andmelting same at high thermal efficiency.

EXAMPLE 1

Powder ferrous raw material, coal (fine powder coal) as powder solidreductant and bentonite (binder) each of a composition shown in Table1-Table 3 were prepared. Table 4 shows the grain size constitution ofthe powder ferrous raw material and the coal.

                  TABLE 1                                                         ______________________________________                                             Chemical composition (mass %)                                                                                         Slag                                      in-                                                                     T.Fe Fe.sub.2 O.sub.3 Fe.sub.3 O.sub.4 FeO Zn C gredient L.O.I.            ______________________________________                                        Iron 67.5   96.3    0.0   0.2  0.006                                                                              0.0  3.5   0.4                              ore A                                                                         Iron 66.0 0.0 82.4 8.2 0.003 0.0 9.4 0.0                                      ore B                                                                         Iron 31.3 38.7 0.0 5.4 1.9 30.2 23.8 0.0                                      work                                                                          dust                                                                          Mill 73.8 0.0 1.9 93.2 0.005 0.0 4.9 0.0                                      scale                                                                       ______________________________________                                         (Note)                                                                        L.O.I. means loss on ignition                                            

                  TABLE 2                                                         ______________________________________                                                 Chemical composition (mass %)                                                 Fixed   Volatile          Total                                         carbon ingredient Ash carbon                                               ______________________________________                                        Coal     64.8    25.8         9.4  78.5                                       ______________________________________                                    

                  TABLE 3                                                         ______________________________________                                                  Composition (mass %)                                                          Gangue                                                                 mineral Fe.sub.2 O.sub.3 L.O.I.                                            ______________________________________                                        Bentonite 78.5         15.4    6.1                                            ______________________________________                                         (Note)                                                                        L.O.I. means loss on ignition                                            

                  TABLE 4                                                         ______________________________________                                        Grain size constitution arter grain size control                              ______________________________________                                        Iron ore A  -325 mesh: 90 mass %                                                Iron ore B -325 mesh: 90 mass %                                               Iron work dust -0.5 mm: 90 mass %, -0.05 mm: 30 mass %                        Mill scale -3 mm: 90 mass %, -1 mm: 50 mass %                                 Coal -200 mesh: 75 mass %, -325 mesh: 60 mass %                             ______________________________________                                    

After mixing them in blending ratios shown in Table 5, the mixed rawmaterials were formed into sheet-like compacts each of 15 mm thicknessand 500 mm width and into sheet-like compacts having the same width buthaving uneven shape on the surface as shown in FIG. 3 by a shaping andcharging device shown in FIG. 2.

Further, for the comparison, a portion of the mixed raw materials waspelletized into green pellets of 18 mm diameter by a pan typepelletizer, and then heated to 115° C., into dry pellets with 90% ormore of water content being removed.

                  TABLE 5                                                         ______________________________________                                              Raw material blending ratio (mass %)                                          Iron                                                                       ore Iron ore Iron work Mill   Water                                           A B dust scale Coal Bentonite added                                        ______________________________________                                        Mixed 71.5   --      --     --   19.0 1.5    8.0                                raw                                                                           material                                                                      P                                                                             Mixed -- 72.0 -- -- 18.5 1.5 8.0                                              raw                                                                           material                                                                      Q                                                                             Mixed 58.6 -- 13.4 -- 18.5 1.5 8.0                                            raw                                                                           material                                                                      R                                                                             Mixed -- -- 25.7 47.5 17.3 1.5 8.0                                            raw                                                                           material                                                                      S                                                                           ______________________________________                                    

The compacts and pellets were put to reducing test under the conditionsshown in Table 6 by using a small-sized high temperatureheating-reduction test furnace shown in FIG. 19 (a) which is a schematicvertical cross sectional view and FIG. 19 (b) which is a cross sectionalview taken along arrow A--A in (a). In Table 6, "mean temperature in thefurnace" is a mean gas temperature in a furnace space after stoppingblowing of oxygen-containing gas to the surface of the compacts orpellets.

As shown in FIG. 19, burners are disposed in two upper and lower stagesin a high temperature heating reduction test furnace 99, and burners ofthe lower stage 101 are used for blowing air as oxygen-containing gas tothe surface of compacts or pellets only for a period while burnablevolatile ingredients are released from the powder solid reductant,thereby burning the burnable volatile ingredients. Use of the lowerstage burners 101 was interrupted at the instance the release of theburnable volatile ingredients ended. On the other hand, upper stageburners 100 are heating burners for keeping the furnace temperature to apredetermined temperature.

The burners are disposed in two upper and lower stages since the testfurnace is a fixed type. In a case of a rotary hearth furnace, theburners may not be arranged in the two stages but may be in one stage.Namely, in the rotary hearth furnace, it may suffice to set the angle ofburners disposed in the generation section of burnable volatileingredients situated downstream of a charging portion for the compactssuch that the oxygen-containing gas hits on the surface of the compacts.Further, it is advantageous to blow the oxygen-containing gas into thefurnace after preheating the gas to about 500 to 600° C. by heatexchange with the exhaust gas.

In the reduction test, the aimed value for the metallizing ratio was setto 92% and a reduction time capable of attaining the aimed value wasmeasured. The results are also shown in Table 6.

                                      TABLE 6                                     __________________________________________________________________________                   Formation of                                                                         Powder solid                                                                         Direct blowing of                                  Mixed Mixed unevenness reductant, oxygen-containing Mean furnace                                                              Reduction Metalizing                                                           material: material: on                                                       the compact disposed                                                          thinly gas to the                                                             compact temperature                                                           time ratio                    type shape surface on hearth surface (° C.) (min) (%)                __________________________________________________________________________    This                                                                            invention                                                                     Case 1 Mixed raw Sheet-like non non non 1300 15 92.0                           material P compact                                                           Case 2 Mixed raw Sheet-like yes non non 1300 15 91.7                           material P compact                                                           Case 3 Mixed raw Sheet-like non yes non 1300 15 92.9                           material P compact                                                           Case 4 Mixed raw Sheet-like non non yes 1300 12 91.6                           material P compact                                                           Comp.                                                                         example                                                                       Case 5 Mixed raw Pellet -- non yes 1300 10 92.0                                material P                                                                   This                                                                          invention                                                                     Case 6 Mixed raw Sheet-like non non yes 1300 11 92.2                           material Q compact                                                           Case 7 Mixed raw Sheet-like yes non yes 1300 12 92.0                           material R compact                                                           Case 8 Mixed raw Sheet-like yes non yes 1300 11 91.9                           material S compact                                                         __________________________________________________________________________

The test was at first conducted under the conditions of case 1. As aresult, it could be confirmed that 92% of metallizing ratio could beattained without pelletization if about 15 min was taken for thereduction time. This shows that the reduction time may be extremelyshorter compared with about 8 to 10 hours of reduction time in a case ofa shaft furnace type direct reduction system using a reduction gasobtained by modifying usual natural gas.

Case 2 show an example in which the upper surface of the sheet-likecompact was made uneven. While the reduction time was substantiallyidentical with case 1, since the amount of the raw material loaded perunit area of the hearth was increased by about 1.9 times, it wasconfirmed that the productivity was increased also to about 1.9 times.This is considered to be attributable to the increase of the heatreceiving area due to the unevenness formed on the upper surface of thesheet-like compact and to the improvement of the temperature elevationrate since the protruded portions are heated from both surfaces althoughthe amount of the raw material powder loaded per unit area of the hearthwas increased to about 1.9 times.

Case 3 is an example in which a sheet-like compact was disposed on thepowder solid reductant laid thinly on the hearth and then put to hightemperature reduction. While it was observed that reduced iron wasslightly adhered on the hearth in other cases, adhesion of reduced orewas not observed at all in the present case.

Case 4 is an example of charging the sheet-like compact into thefurnace, then supplying air to the surface of the sheet-like compactonly for about 2 min in which burnable volatile ingredients in the coalcontinued are kept to be released and burning the burnable volatileingredients released from the coal also on the surface of the sheet-likecompact. As a result, the reduction time was further shortened by 3 minfrom 15 min in case 1 to 12 min and it could be confirmed the merit ofheating and elevating temperature while taking place combustion of theburnable volatile ingredients released from the sheet-like compact alsoon the surface of the sheet-like compact.

Case 5 is an example of using conventional dry pellet. The reductiontime was 10 min which was somewhat shorter compared with the case 4. Itis considered that while the pellets were used after drying, thesheet-like compact was used as it is not dried. However, in a case ofusing the pellet, since it requires drying for a relatively long periodof time at the outside of the furnace, the processing time was consumedso much and this can not be said advantageous. Accordingly, it can besaid that the method of the present invention using the powder rawmaterial in the form of the sheet-like compact is a reduction methodcomparable with the case of using the pelletized material.

Case 6 is an example of using ore B (iron oxide in the formed ofmagnetite) shown in Table 1. The reduction time was 11 min, which wassomewhat shorter compared with case 4 (using ore A with the iron oxidein the form of hematite). This is assumed that while both reduction ofmagnetite and hematite into metallic iron are endothermic reductions,the reaction heat per iron atom is smaller in the magnetite by about4760 kcal/kmol, so that temperature lowering is small in the compactand, as a result, the reduction reaction was promoted.

Case 7 is an example of using ferrous raw material comprising ore Ablended with iron work dust. Case 8 is an example of using ferrous rawmaterial comprising dust and mill scale blended therewith. The reductiontime in each of the cases was about 12 min and 11 min, which wassubstantially identical with the case 4 of using iron ore.

Further, dezinc ratio in case 7 using Zn-containing dust was about 92%and the dezinc effect according to the method of the present inventioncould be confirmed.

It is considered that although the mixed raw material S was somewhatcoarser, the reduction time was not changed so much in case 8, becauseiron oxide in the mixed raw material S was FeO and the reduction ratiowas about 30% on the basis of Fe₂ O₃, so that the reduction amount downto the metallic iron may be smaller as well as that the amount ofendothermic reduction per iron atom from FeO into metallic iron isdecreased by about 20590 kcal/kmol compared with the case of Fe₂ O₃ andthe temperature lowering in the sheet-like compact was small and, as aresult, the reduction reaction was promoted.

EXAMPLE 2

Powder iron ore and coal (fine powder coal) as the powder solidreductant having the composition and the grain size constitution asshown in Table 7-Table 9 blended in a blending ratio shown in Table 10was prepared.

                  TABLE 7                                                         ______________________________________                                        Kind of   Chemical composition (mass %)                                       powder ferrous                      Slag                                        raw material T.Fe Fe.sub.2 O.sub.3 Fe.sub.3 O.sub.4 FeO ingredient                                                     L.O.I.                             ______________________________________                                        Iron ore  67.5   96.3    0.0   0.2  2.0    0.4                                ______________________________________                                         (Note)                                                                        L.O.I. means loss on ignition                                            

                  TABLE 8                                                         ______________________________________                                        Kind of    Chemical composition (mass %)                                      powder solid                                                                             Fixed   Votatile         Total                                       reductant carbon ingredient Ash carbon                                      ______________________________________                                        Coat       64.8    25.8        9.4  78.5                                        Coke 88.0 0.2 11.0 88.7                                                     ______________________________________                                    

                  TABLE 9                                                         ______________________________________                                        Grain size constitution after grain size control                              ______________________________________                                        Iron ore -325 mesh: 90 mass %                                                   Coal -200 mesh: 75 mass %, -325 mesh: 60 mass %                               Coke 10 ˜ 30 mm: 30 mass %, 30 ˜ 60 mm: 70 mass %               ______________________________________                                    

                  TABLE 10                                                        ______________________________________                                        Raw material blending ratio (mass %)                                            Iron ore         Coal       Total                                           ______________________________________                                        79.7           20.3       100.0                                               ______________________________________                                    

As the test facility, a small-sized molten iron manufacturing testfacilities described above shown in FIG. 17 was used. That is thefacility comprises a rotary hearth furnace 11 as a preliminary reductionfurnace, a shaft furnace 85 as a smelting furnace and a raw materialreceiving hopper 26, a mixer 22 and a waste heat recovery heat exchanger34 and the like.

Powder ore 27, reductant 28 (fine powder coal) and a binder 29 receivedin a raw material receiving hopper 26 were taken out each by apredetermined amount from respective hoppers and charged in the mixer22, sufficiently mixed with addition of a small amount of water and thenthe mixture was charged into the rotary hearth furnace.

The mixture was charged into the hearth by compacting them into asheet-like shape by the shaping/charging device shown in FIG. 2 and thenplacing on the hearth. The thickness of the sheet-like compact wasdefined to 15 mm.

Air, including combustion air, was used after preheating to 600° C. byheat exchange with exhaust gas from the rotary hearth furnace. After theend of the evolution of the burnable volatile ingredients, the averagegas temperature in the furnace space was set to about 1300° C. Further,the aimed value for the metallizing ratio of reduced iron was defined to92%.

The reduced iron obtained from the rotary hearth furnace 11 was takenout at about 1150° C. to the outside of the furnace, slightly pulverizedcoarsely and then charged from above the shaft furnace 85. Coke 86 wascharged together with lime stone 87 from above the shaft furnace. Thelime stone was used in such an amount so as to provide the basidity ofslag at 1.25.

In addition to the case of blowing air 89 and oxygen 90 from tuyeres 88,a case of blowing fine powder coal 92 to thereby reduce the consumptionamount of coke which is more expensive compared with the fine powdercoal was also studied.

Molten iron was discharged together with slags from a tap hole disposedto a lower portion of the furnace.

The exhaust gas 31 from the shaft furnace 85 was removed with dust by acyclone 93 and a portion thereof was blown from a burners 25 as fuelused in the rotary hearth furnace 11, while other portions wererecovered as fuel for other facilities.

The test was conducted on six cases shown in Table 11.

                                      TABLE 11                                    __________________________________________________________________________    Furnace                                                                             Item             Case 1                                                                            Case 2                                                                            Case 3                                                                             Case 4                                                                             Case 5                                                                            Case 6                           __________________________________________________________________________    Preliminary                                                                         Placing of mixture on the preliminary                                                          Pellet                                                                            Sheet-                                                                            Sheet-                                                                             Sheet-                                                                             Sheet-                                                                            Sheet-                             reduction reduction furnace hearth used like like like like like                                                          furnace Powder solid                                                         reductant, laid thinly -- --                                                  Practiced -- -- --                  on hearth                                                                     Unevenness formed on the upper -- -- -- Practiced -- --                       surface of the sheet-like compact                                             Ore (kg/pt) 1370 1370 1370 1370 1370 1370                                     Air preheating temperature (° C.) 600 600 600 600 600 600                                                          Amount of air (Nm.sup.3                                                     /pt) 1789 1743 1743 1621                                                      1739 1764                           Amount of smelting 404 404 404 404 404 241                                    furnace exhaust gas used (Nm.sup.3 /pt)                                       Rduction time in preliminary 10 15 15 15 15 15                                reduction furnace (min)                                                       Metallizing ratio of reduced iron (%) 92.0 92.0 92.0 91.8 92.0 92.0                                                       Reduced iron discharging                                                    temp. (° C.) 1150                                                      1150 1150 1150 1150 1150                                                        Securing of Reduced iron                                                    to hearth Secured Secured                                                     Not Secured Secured Secured                                                      slightly slightly at all                                                   slightly slightly slightly                                                     Smelting Reduced iron                                                        discharging temp. (°                                                   C.) 650 650 650 650 650 650                                                    furnace Coke (kg/pt) 341                                                     341 341 312 287 107                 Fine powder coal (kg/pt) 0 0 0 0 0 329                                        Fuel (kg/pt) 341 341 341 312 287 436                                          Oxygen (Nm.sup.3 /pt) 126 129 129 116 72 265                                  Air (Nm.sup.3 /pt) 562 566 566 509 622 47                                     Air temperature (° C.) 25 25 25 25 600 600                             Molten iron temperature (° C.) 1500 1500 1500 1500 1500 1500                                                       Molten iron [C] (%) 4.6                                                     4.6 4.6 4.6 4.6 4.6                 Molten iron [S] (%) 0.02 0.02 0.02 0.02 0.02 0.02                             Slag (kg/pt) 168 168 168 163 159 178                                          Slag basidity (-) 1.25 1.25 1.25 1.25 1.25 1.25                            __________________________________________________________________________     (Note)                                                                        "Sheetlike" means Sheetlike compact                                      

Case 1 indicates a test in a case of pelletting a raw material mixtureby an existent method in which the reduction time in the rotary hearthfurnace was 10 min.

Case 2 shows an example of compacting the raw material mixture into asheet-like shape and it was confirmed that reduced iron of 92%metallizing ratio was obtained if the reduction time was set to about 15min. This shows that the reduction time may be extremely shortercompared with about 8 to 10 hours of reduction time in a case of a shaftfurnace type direct reduction system using reduction gas obtained bymodifying usual natural gas.

Case 3 is an example in which a sheet-like compact was disposed on thepowder solid reductant laid thinly on the hearth and then put to hightemperature reduction. While it was observed that reduced iron wasslightly adhered on the hearth in other cases, adhesion of reduced orewas not observed at all.

Case 4 show an example in which the upper surface of the sheet-likecompact was made uneven as shown in FIG. 3. While the reduction time wassubstantially identical with case 2, since the amount of the rawmaterial loaded per unit area of the hearth was increased by about 1.9times, it was confirmed that the productivity was increased also toabout 1.9 times. This is considered to be attributable to the increaseof the heat receiving area due to the unevenness formed on the uppersurface of the sheet-like compact and to the improvement of thetemperature elevation rate since the protruded portions are heated fromboth surfaces although the amount of the raw material powder loaded perunit area of the hearth was increased to about 1.9 times.

In the cases 1-4 above, oxygen enriched air at a normal temperature wasused for the blowing condition, operation was conducted at a theoreticalburning temperature before the tuyeres of 2,500° C., and reduced iron atabout 650° C. was charged into the shaft furnace thereby enabling toproduce molten iron of good quality containing 4.6 wt % C and 0.02 wt %sulfur.

Case 5 is an example of blowing air while heating to about 600° C., inwhich the amount of oxygen used was reduced to 57 Nm³ /pt compared withthe case 2 and the combustion ratio of the shaft furnace was also lowerand the effect could be confirmed.

Case 6 shows an example of blowing fine powder coal to the tuyeres.Although the combustion ratio was increased slightly, the coke ratio waslowered to 170 kg/pt, which was reduced to about 1/3 compared with othercases, and the effect could be confirmed.

EXAMPLE 3

Powder iron ore, coal (fine powder coal) as the powder solid reductanthaving the composition and the grain size constitution as shown in Table7-Table 9 used in Example 2, and bentonite shown in Table 3 used inExample 1 blended in a blending ratio shown in Table 12 was prepared.

                  TABLE 12                                                        ______________________________________                                        Raw material blending ratio (mass %)                                               Iron ore                                                                              Coal          Bentnaite                                                                            Total                                       ______________________________________                                        75.7     19.3          5.0      100.0                                         ______________________________________                                    

As the test facility, a small-sized molten iron manufacturing testfacilities described above shown in FIG. 18 was used. That is thefacility comprises a rotary hearth furnace 11 as a preliminary reductionfurnace, a in-bath smelting furnace 94 as a smelting furnace and a rawmaterial receiving hopper 26, a mixer 22 and a waste heat recovery heatexchanger 34 and the like.

Fine iron oxide 27 (powder iron ore), reductant 28 (fine powder coal)and a binder 29 received in a raw material receiving hopper 26 weretaken out each by a predetermined amount from respective hoppers andcharged in the mixer 22, sufficiently mixed with addition of a smallamount of water and then the mixture was charged into the rotary hearthfurnace.

The mixture was charged into the hearth by compacting it into asheet-like shape by the shaping/charging device shown in FIG. 2 and thenplacing on the hearth. The thickness of the sheet-like compact wasdefined to 15 mm.

Air, including combustion air, was used after preheating to 600° C. byheat exchange with an exhaust gas from the rotary hearth furnace. Afterthe end of the evolution of the burnable volatile ingredients, theaverage gas temperature in the furnace space was set to about 1300° C.Further, the aimed value for the metallizing ratio of reduced iron wasdefined to 92%.

The reduced iron obtained from the rotary hearth furnace 11 was takenout at about 1150° C. to the outside of the furnace, slightly pulverizedcoarsely and then charged from above the in-bath smelting furnace 94.Carbon material 86 (coal) was charged together with flux 87 (lime stone)from above the in-bath smelting furnace. The lime stone was used in suchan amount so as to provide the basidity of slag at 1.25.

Molten iron was discharged together with slags from a tap hole disposedto a lower portion of the furnace.

A portion of the exhaust gas 31 from the in-bath smelting furnace 94 wasused as fuel used in the rotary hearth furnace 11, while other portionswere recovered as fuel for other facilities.

The test was conducted on four cases shown in Table 13.

                                      TABLE 13                                    __________________________________________________________________________    Furnace                                                                             Item              Case 1                                                                             Case 2                                                                             Case 3                                                                             Case 4                                 __________________________________________________________________________    Preliminary                                                                         Placing of mixture on the preliminary                                                           Pellet                                                                             Sheet-like                                                                         Sheet-like                                                                         Sheet-like                               reduction reduction furnace hearth used compact compact compact                                                     furnace Powder solid reductant,                                              laid thinly -- -- Practiced --                                                  on hearth                               Unevenness formed on the upper surface -- -- -- Practiced                     of the sheet-like compact                                                     Ore (kg/pt) 1436 1436 1436 1436                                               Air preheating temperature (° C.) 600 600 600 600                      Amount of air (Nm.sup.3 /pt) 2145 2145 2145 2144                              Amount of smelting  538 538 538 538                                           furnace exhaust gas used (Nm.sup.3 /pt)                                       Rduction time in preliminary 10 15 15 15                                      reduction furnace (min)                                                       Metallizing ratio of reduced iron (%) 92.0 92.0 92.0 91.8                     Reduced iron discharging temp. (° C.) 1150 1150 1150 1150                                                    Securing of Reduced iron to                                                 hearth Secured Secured Not Secured         slightly slightly at all slightly                                           Smelting Reduced iron discharging temp. (° C.) 800 800 800 800                                               furnace Coal 282 282 282 283                                                   Oxygen (Nm.sup.3 /pt) 282 282                                               282 283                                   Molten iron temperature (° C.) 1500 1500 1500 1500                     Molten iron [C] (%) 4.0 4.0 4.0 4.0                                           Molten iron [S] (%) 0.05 0.05 0.05 0.05                                       Slag (kg/pt) 177 177 177 177                                                  Slag basidity (-) 1.25 1.25 1.25 1.25                                      __________________________________________________________________________

Case 1 indicates a test in a case of pelletting a raw material mixtureby an existent method in which the reduction time in the rotary hearthfurnace was 10 min.

Case 2 shows an example of compacting the raw material mixture into asheet-like shape and it was confirmed that reduced iron of 92%metallizing ratio was obtained if the reduction time was set to about 15min. This shows that the reduction time may be extremely shortercompared with about 8 to 10 hours of reduction time in a case of a shaftfurnace type direct reduction system using reduction gas obtained bymodifying usual natural gas.

Case 3 is an example in which a sheet-like compact was disposed on thepowder solid reductant laid thinly on the hearth and then put to hightemperature reduction. While it was observed that reduced iron wasslightly adhered on the hearth in other cases, adhesion of reduced orewas not observed at all.

Case 4 show an example in which the upper surface of the sheet-likecompact was made uneven as shown in FIG. 3. While the metallizing ratioand the reduction time were substantially identical with those in case2, since the amount of the raw material loaded per unit area of thehearth was increased by about 1.9 times, it was confirmed that theproductivity was increased also to about 1.9 times. This is consideredto be attributable to the increase of the heat receiving area due to theunevenness formed on the upper surface of the sheet-like compact and tothe improvement of the temperature elevation rate since the protrudedportions are heated from both surfaces although the amount of the rawmaterial powder loaded per unit area of the hearth was increased toabout 1.9 times.

In any of the cases 1-4 above, reduced iron at about 800° C. was chargedinto the in-bath smelting furnace thereby enabling to produce molteniron of good quality containing 4.0 wt % C and 0.05 wt % sulfur.

EXAMPLE 4

Powder iron ore shown in Table 14 and powder coal shown in Table 15 wereused and blended in a blending ratio shown in Table 16, mixed and thencompacted into a sheet-like shape of a size shown in the same table by adouble roll compressor, charged in a rotary hearth furnace by way of acharging chute and baked into reduced iron. The specification for thefacility of the rotary hearth furnace used and the operation conditionsare shown in Table 17.

                  TABLE 14                                                        ______________________________________                                        Powder                         Grain size                                     iron raw material                                                                       Chemical composition (mass %)                                                                      -74    -44                                     Kind Brand    Fe.sub.2 O.sub.3                                                                      SiO.sub.2                                                                          Al.sub.2 O.sub.3                                                                    FeO  ZnO  μm                                                                              μm                         ______________________________________                                        Iron Pellet feed                                                                            97.0    1.0  0.5   0.1  0.001                                                                              81%  42%                             ore MBR                                                                     ______________________________________                                    

                                      TABLE 15                                    __________________________________________________________________________    Powder                                                                          solid reductant Chemical composition (mass %) Grain size                    Kind                                                                             Brand C  H  Fe.sub.2 O.sub.3                                                                  SiO.sub.2                                                                         Al.sub.2 O.sub.3                                                                  VM  -74 μm                                                                         -44 μm                                  __________________________________________________________________________    Coal                                                                             Woodland                                                                            74.3                                                                             4.4                                                                              1.0 5.9 3.1 34.2                                                                              86% 44%                                        __________________________________________________________________________     (Note)                                                                        VM: Volatile ingredient                                                  

                  TABLE 16                                                        ______________________________________                                        Com-                                                                            pacted  Water content  Brend- Water                                           raw  after  ing ratio content                                                 material  compaction  (mass (mass                                             shape Size (mass %) Brand %) %)                                             ______________________________________                                        Sheet-like                                                                           5 mm(width) ×                                                                      11         MBR   77    8                                      compact 15 mm  Wood- 21 9                                                      (thickness)  land                                                               Load tar 2 0                                                             ______________________________________                                    

                  TABLE 17                                                        ______________________________________                                        Main specification for                                                          rotary hearth furnace Operation condition                                   ______________________________________                                        Effective outer diameter: 40 m                                                                  Speed of rotary hearth: 0.080 rpm                             Effective inner diameter: 30 m Furnace temperature: 1300° C.                            Effective width: 5.0 m Furnace combustion gas: LPG                            Distance from furnace: 2.1 m                                 ceiling to hearth                                                           ______________________________________                                    

Upon production of reduced iron, iron powder remaining on the hearth wasremoved by the method shown in case 1-case 6 in Table 18, or theremaining reduced iron powder on a hearth was prevented, and the effectof the present invention was evaluated based on the metallizing ratio ofthe obtained reduced iron. Case 1 shows an existent example in which thereduced iron was discharged by the screw feeder described above shown inFIG. 10 and then the operation was conducted without removing thereduced iron powder.

                                      TABLE 18                                    __________________________________________________________________________    Reduced iron powder                Metallizing                                  removing device Specification for facility ratio (%) Remarks                __________________________________________________________________________    Case 1                                                                            non           --               85.6  Existent                                   Example                                                                   Case 2 Gas jetting nozzle Nozzle width:  5 m 93.1 Example for                  (FIG. 12) Nozzle moving speed: 20 m/min  the invention                       Case 3 Rotary type cleaning Width of rotary cleaning brush group:  5 m                                               91.4 Example for                        brush   the invention                                                         (FIG. 13) Moving speed of brush group: 20 m/min                              Case 4 Reciprocating scraper Scraper width:  5 m 90.6 Example for                                                      (FIG. 14) Scraper moving                                                    speed: 20 m/min  the invention                                                 Case 5 Suction food Disposed in                                              one row in the lateral 94.5                                                   Example for                             (FIG. 15) direction of a hearth  the invention                                 Suction port: width 5 m. length 0.3 m                                       Case 6 Scraper type gate Disposed in one row in the lateral 90.7                                                     Example for                             (FIG. 16) direction of a hearth  the invention                                 (Gate width 5 m. thickness 10 mm)                                             Contact pressure (urging puressure):  2 kgf/cm.sup.2                      __________________________________________________________________________

The metallizing ratio of the reduced iron in each of the cases is shownin Table 18, and the metallizing ratio of the reduced iron could bemaintained higher in the examples of the present invention as comparedwith the existent examples. This is because the uneven combustion wasreduced as a result of removing the reduced iron powder remaining on thehearth on every discharge of the reduced iron or as a result ofpreventing the residue of the reduced iron powder on the hearth.

EXAMPLE 5

The powder iron ore shown in Table 14 and the powder coal shown in Table15 of Example 4 were used and blended in the blending ratios shown inTable 16, mixed and then compacted into sheet-like compacts of a sizeshown in the same table by a double roll compressor, charged in a rotaryhearth furnace by way of a charging chute and baked into reduced iron.The specifications for the facility and the operation conditions of therotary hearth furnace used are identical with those in Example 4.

The reduced iron was discharged by the methods shown in case 1-case 3 inTable 19 and the effect of the present invention was evaluated by themetallizing ratio of the obtained reduced iron.

                  TABLE 19                                                        ______________________________________                                                                      Metalliz-                                          Discharging  ing Remarks                                                      device Specification for facility ratio (%)                                ______________________________________                                        Case Screw feeder                                                                            --             85.6   Existent                                   1    Example                                                                  Case Guide fennce -- 90.1 Example for                                         2 (FIG. 11   the invention                                                     c, d)                                                                        Case Pusher Pusher width: 5 m 92.1 Exanple for                                3 (FIG. 11 Pusher moving speed:  the invention                                 a, b) 20 m/min                                                             ______________________________________                                    

The metallizing ratio of the reduced iron (average value) for each caseis shown in Table 19. The metallizing ratio could be maintained at ahigh level in the examples of the present invention compared withexistent examples. This is considered to be attributable to that thereduced iron did not remain on the hearth and reoxidation could beprevented in the examples of the present invention.

EXAMPLE 6

The powder iron ore shown in Table 14 and the powder coal shown in Table15 of Example 4 were used and blended in the blending ratios shown inTable 16, mixed and then compacted into pellets or a sheet-like compactsshown in Table 20, charged in a rotary hearth furnace by way of acharging chute and baked into reduced iron. The specifications for thefacility and the operation conditions of the rotary hearth furnace usedare identical with those in Example 4, except for adjusting the speed ofthe rotary hearth furnace such that it took 9 min from charging chargingof the raw material to discharge of products.

                  TABLE 20                                                        ______________________________________                                        Shape of the                   Blending                                                                             Water                                     compacted   ratio content                                                     material Size Brand (mass %) (mass %)                                       ______________________________________                                        Pellet    15 mm       MBR      78     8                                         (with no binder) (spherical Woodland 22 9                                      diameter)                                                                    Pellet 15 mm MBR 77 8                                                         (with binder) (spherical Woodland 21 9                                         diameter) Bentnite 2 0                                                       Sheet-like 5 m(width) × MBR 78 8                                        compact 15 mm(thickness) Woodland 22 9                                        (with no binder)                                                            ______________________________________                                    

A pellet of 15 mm diameter was prepared by using a pan type pelletizerof 7.5 m diameter in accordance with the production steps shown in FIG.1, and charged into a rotary hearth furnace to produce reduced iron. Thewater content of the pellet after compaction was set to 11 mass %.

The metallizing ratio of the obtained reduced iron is shown for case Aand case B in Table 21. Case A and Case B are examples of using afretting mill used so far as a mixer (existent example).

Reduced iron was produced in accordance with the production steps shownin FIG. 20, by using a high speed stirring mixer at a rotational speedof 300 rpm as a mixer 22, collectively mixing and processing powder ironore 3, powder coal 4 and water 7 such that the water content of the rawmaterial was settled constant at 11 mass %, compacted into a sheet-likeshape by a double roll compressor 10 (shown in an enlarged scale)disposed just above the raw material charging section 12 of the rotaryhearth furnace 11 and then charged by a charging chute 102 onto therotary hearth furnace 13.

The metallizing ratio of the obtained reduced iron is shown for case C,case D1 and case D2 in Table 21. Case C is an example of using afretting mill used so far as a mixer (examples of the invention), bothof cases D1, D2 are examples of using a high speed stirring mixer(examples of the invention), D1 is an examples of using the powder coalas it is and D2 is a case of previously applying a drying treatment.

A higher metallization ratio is shown in the examples of the presentinvention using the high speed stirring mixer. Further, a highermetallization ratio was obtained in a case of previously applying thedrying treatment to the powder coal.

The relationship between the water content of the raw material and themetallizing ratio of the reduced iron is shown in FIG. 21. From theresult, it can be seen that a high metallizing ratio was obtained at thewater content of 6 to 18 mass % in Case D1.

                                      TABLE 21                                    __________________________________________________________________________                   Water content                                                                        Mixer  Metallizing                                         Molding  in coal (rotaitional ratio                                           machine Binder (mass %) speed, rpm) (%)                                    __________________________________________________________________________    Case A                                                                             Pelletizer                                                                          non 9      Fretting mill                                                                        62    Existent                                           Example                                                                 Case B Pelletizer Bentnite 9 Fretting mill 69 Existent                              Example                                                                 Case C Double roll non 9 Fretting mill 89 Example for                               the invention                                                           Case D1 Double roll non 9 High speed 94 Example for                               stirring mixer  the invention                                                 (300)                                                                     Case D2 Double roll non dried High speed 98 Example for                           stirring mixer  the invention                                                 (300)                                                                   __________________________________________________________________________

EXAMPLE 7

Powder iron ore shown in Table 22 and power coal shown in Table 23 wereused for producing reduced iron under the conditions shown in Table 24.The metallizing ratio of the reduced iron in this case was determinedand the effect of the present invention was evaluated.

                  TABLE 22                                                        ______________________________________                                        Powder                                                                          iron raw material Chemical composition (mass %) Grain size                  Kind  Brand    Fe.sub.2 O.sub.3                                                                      SiO.sub.2                                                                          Al.sub.2 O.sub.3                                                                    FeO  ZnO  -1 mm                             ______________________________________                                        Iron  Pellet feed                                                                            97.0    1.0  0.5   0.1  0.001                                                                              80%                                 ore MBR                                                                       Iron Carajas 96.2 0.5 0.8 0.1 0.001 43%                                       ore                                                                         ______________________________________                                    

                  TABLE 23                                                        ______________________________________                                        Powder                                                                          solid reductant Chemical composition (mass %) Grain size                    Kind Brand   C      H   Fe.sub.2 O.sub.3                                                                    SiO.sub.2                                                                          Al.sub.2 O.sub.3                                                                    VM   -1 mm                           ______________________________________                                        Coal Wood-   74.3   4.4 1.0   5.9  3.1   34.2 13%                                land                                                                       ______________________________________                                         (Note)                                                                        VM: Volatile ingredient                                                  

                  TABLE 24                                                        ______________________________________                                                Powder      Powder                                                      Test item raw material solid reductant Remark                               ______________________________________                                        Ingredient of                                                                         Iron ore of 79%                                                                           Coal(Woodland)                                                                            Existent example:                               powder iron various brand 21% (grain size: Bentnaite 2%                       ore (grain size: d.sub.50 = 60 μm) Iron ore(MBR) 77%                       (Al.sub.2 O.sub.3 + d.sub.50 = 60 μm)  Coal(Woodland)                      SiO.sub.2)   21% (grain size:                                                 altered test   d.sub.50 = 60 μm)60 μm)                                  Mixing test Iron ore(MBR) Coal(Woodland)                                      of power 79% 21%                                                              coal to fine  Water content 9%                                                powder iron                                                                   ore                                                                         ______________________________________                                    

The reduced iron was manufactured in accordance with the productionsteps shown in FIG. 1 by shaping the raw material into sheet-likecompacts by a double roll compressor having double rolls of 5.0 mdiameter, charging then by a charging chute into a rotary hearth furnaceand baking them. The specifications for the facility and the operationconditions of the rotary hearth used are identical with those in Example6.

Test of Changing Ingredients (Al₂ O₃ +SiO₂) of the Powder Iron Ore

Powder iron ores of various brands having different contents for thetotal of Al₂ O₃ and SiO₂, were used and the effect of the ingredients(Al₂ O₃ +SiO₂) contained in the powder iron ore on the metallizing ratiowas investigated. For the comparison, the effect of the ingredient (Al₂O₃ +SiO₂) in a case of adding bentonite (clay) on the metallizing ratiowas also investigated.

The results is shown in FIG. 22. In the figure, "" shows a case ofusing powder iron ore having different contents of the ingredients (Al₂O₃ +SiO₂), and "◯" shows a case of varying the content of the ingredient(Al₂ O₃ +SiO₂) in the raw material mixture by adding bentonite.

As apparent from the result, when the content of the ingredient (Al₂ O₃+SiO₂) was changed by changing the brand of the powder iron ore, themetallizing ratio of the reduced iron was increased abruptly when thecontent exceeds 4 mass %. On the contrary, when the content of theingredient (Al₂ O₃ +SiO₂) was changed by adding bentonite (clay), theratio was increased in proportion with the addition amount of bentonitebut no abrupt increase was observed.

Test of Mixing Powder Coal to Fine Powder Iron Ore

The effect of the ratio of grains having the grain size of the coal(grain size: 0.1-1 mm ratio) on the metallizing ratio of the reducediron was investigated by using fine powder iron ore in which 80% ofgrains being under 0.1 mm as the powder iron raw material (pellet feedMBR) and using coal with 9 mass % of water content as the powder solidreductant, and controlling the grain size by pulverizing the coal whilecontrolling gaps by an impact mill pulverizer thereby changing the ratioof grains having the grain size from 0.1 to 1 mm (grain size: 0.1-1 mmratio). conducted in the same manner also for a case of adding 15 partsby weight of iron ore (carajas) to 100 parts by weight of coal andmixing and pulverizing them under the same condition for the gap controlby the impact mill pulverizer.

The result of the investigation is shown in FIG. 23. In the figure, ""shows a case of pulverizing the coal alone and "◯" shows a case ofpulverizing the coal with addition of iron ore. In each of the cases, ahigh metallizing ratio was shown when the ratio of the coal with thegrain size from 0.1 to 1.0 mm was not less than 50%.

Further, even when the pulverizing conditions of the impact mill wereidentical, deposition of the coal to the pulverizer was reduced,efficient pulverization was possible, the ratio of the coal with a grainsize from 0.1 to 1.0 mm could be increased and a higher metallizingratio was shown in a case of adding the iron ore and mixing andpulverizing the same ("◯").

EXAMPLE 8

The powder iron ore and the powder coal having the composition and thegrain size used in Example 4 were blended at a blending ratio shown inTable 25, mixed and then compacted into pellets or sheet-like compactsof the size shown in Table 25. Reduced iron was manufactured by usingthe compacted raw material under the conditions for case 1-case 3 shownin Table 26, and the productivity was determined to evaluate the effectof the present invention.

The specifications for the facility and the operation conditions of therotary hearth used were identical with those in Example 4 except forcontrolling the rotary hearth speed such that the metallizing ratio ofthe products was 92%. That is, if the metallizing ratio of the reducediron was lower than the aimed value (92%), the rotational speed waslowered and the baking time was extended to increase the metallizingratio. In this case, the productivity was lowered. On the contrary, ifthe metallizing ratio was higher than the aimed value, the rotationalspeed was increased and the baking time was shortened to lower themetallizing ratio to the aimed value. In this case, the productivity wasimproved.

                                      TABLE 25                                    __________________________________________________________________________                     Water content                                                                              Blending                                                                           Water                                        Shape of the  after compaction  ratio content                                 compacted material Size (mass %) Brand (mass %) (mass %)                    __________________________________________________________________________    Pellet   20 mm   11      MBR  77   8                                             (spherical  Woodland 21 9                                                     diameter)  Bentnite 2 0                                                      Sheet-like 5 m(width) × 11 MBR 77 8                                     compact 15 mm(thickness)  Woodland 21 9                                          Road tar 2 0                                                             __________________________________________________________________________

                  TABLE 26                                                        ______________________________________                                             Shape of                                                                    raw  Productivity                                                             material Shape of charging shoot (t/D · m.sup.2)                  ______________________________________                                        Case Pellet   Plate shoot(raw material,                                                                    1.05    Existent                                   1  shaped out of the  Example                                                   furnace)                                                                    Case Sheet-lik Curved shoot 2.08 Example for                                  2 compact   the invention                                                     Case Sheet-lik Top end shoot 2.24 Example for                                 3 compact   the invention                                                   ______________________________________                                    

Case 1 is an example of manufacturing pellets of 20 mm diameter by acustomary method in accordance with the production steps shown in FIG. 1by using a pan-like type pelletizer of 7.5 m diameter and charging thesame by a plate-type chute in the rotary hearth furnace (existentexample). Case 2 and Case 3 are examples of disposing a double rollcompressor just above the raw material charging portion of the rotaryhearth furnace, in which case 2 shows an example of charging thematerial by using the charging chute having a concaved top end and case3 is an example of charging the pellet by using the top end chuteconnected at a hinge to the charging device.

As a result of comparison for the operations in each of the cases, sinceless impact force was exerted on the compacted raw material till theyare charged to the hearth in the example of the present inventioncompared with the existent examples, the powder were less formed,undesired effect due to the deposition of the powder in the furnace wasreduced and the productivity of the reduced iron was improved.

EXAMPLE 9

The powder iron ore and the powder coal having the composition and thegrain size used in Example 4 were blended at a blending ratio shown inTable 27, mixed and then compacted into pellets or sheet-like compactsof the size shown in Table 27. Reduced iron was manufactured by usingthe compacted raw material under the conditions for case 1-case 5 shownin Table 28, and the productivity was determined to evaluate the effectof the present invention.

The specifications for the facility and the operation conditions of therotary hearth used were identical with those in Example 4 except forcontrolling the rotary hearth speed such that the metallizing ratio ofthe products was 92%.

                                      TABLE 27                                    __________________________________________________________________________                     Water content                                                                              Blending                                                                           Water                                        Shape of the  after compaction  ratio content                                 compacted material Size (mass %) Brand (mass %) (mass %)                    __________________________________________________________________________    Pellet   20 mm   11      MBR  77   8                                             (spherical  Woodland 21 9                                                     diameter)  Bentnite 2 0                                                      Sheet-like 5 m(width) × 16 MBR 78 8                                     compact 15 mm(thickness)  Woodland 22 9                                     __________________________________________________________________________

                  TABLE 28                                                        ______________________________________                                             Shape of Shape of           Pro-                                            raw charging  ductivity                                                       material shoot Film or belt (t/D · m.sup.2)                       ______________________________________                                        Case Pellet   (shaped out                                                                             --       1.00   Existent                                1  of the   Example                                                             furnace)                                                                    Case Sheet-lik FIG.8 (a) Polyethylene of 2.58 Example                         2 compact  0.1 mm  for the                                                       thickness  invention                                                       Case Sheet-lik FIG.8 (a) Paper of 30 2.54 Example                             3 compact  g/m.sup.2  for the                                                      invention                                                                Case Sheet-lik FIG.8 (b) Rubber belt of 2.23 Example                          4 compact  10 mm  for the                                                        thickness  invention                                                       Case Sheet-lik FIG.8 (b) Steel of 2.44 Example                                5 compact  1 mm thickness  for the                                                 invention                                                              ______________________________________                                    

Case 1 is an example of manufacturing pellets of 20 mm diameter in thesame manner as in Example 8 and charging them by a plate-type shoot intoa rotary hearth furnace.

Case 2 and Case 3 are examples of using the charging device shown inFIG. 8(a), compacting the raw material mixture and film together by adouble-roll compressor into sheet-like compacts by placing thecompressed raw material on the film, and placing the sheet-like compacttogether with the film on the hearth. As the film, polyethylene of 0.1mm thickness and paper of 30 g/m2 were used. In this case, the thicknessof the sheet-like compact charged on the hearth was made constant at 15mm. Further, the rotational speed of the double-roll was set so as tosynchronize with the moving speed of the hearth.

Case 4 and case 5 are examples of using the charging device shown inFIG. 8(b), compacting the raw material mixture and belt together by adouble roll compressor into sheet-like compacts by placing the compactedraw material was placed on the belt, separating the belt and thesheet-like compact near the hearth and placing the sheet-like compact onthe hearth. A rubber belt of 10 mm thickness was used as the belt incase 4, and a steel belt of 2 mm thickness was used as the belt in case5. The thickness of the sheet-like compact and the control for therotational speed of the double roll were identical with those in thecase of using the film.

In the operation, the rotational speed of the hearth was controlled suchthat the metallizing ratio of the reduced iron was 92% like that inExample 8.

As a result of comparison for the operations in each of the cases, theraw material could be baked stably with no unevenness and theproductivity for the reduced iron was improved in the examples of thepresent invention as compared with the existent example. This is becausethe raw material mixture could be charged at a high filling ratio in asheet-like shape on the furnace.

EXAMPLE 10

The powder iron ore and the powder coal having the composition and thegrain size used in Example 4 were blended at the blending ratio shown inTable 25 of Example 8, mixed and then compacted into pellets orsheet-like compacts of the size shown in Table 25. Reduced iron wasmanufactured by using the compacted raw material under the conditionsfor case 1-case 4 shown in Table 29, and the productivity was determinedto evaluate the effect of the present invention. The specifications forthe facility and the operation conditions of the rotary hearth used wereidentical with those in Example 4 except for controlling the rotaryhearth speed such that the metallizing ratio of the products was 92%.

                                      TABLE 29                                    __________________________________________________________________________        Shape  Disposing position of                                                                    Disposing position                                                                     Productivity                                      of raw material double roll compressor press roll (t/D ·                                               m.sup.2)                                 __________________________________________________________________________    Case 1                                                                            Pellet (shaped out of                                                                           --       1.05  Ex.                                          the furnace)                                                                Case 2 Sheet-lik Above the raw material Upstream to the 2.08 Iv.                                                   compact charging portion rotary                                             hearth                                       (single unit)                                                               Case 3 Sheet-lik Above the raw material Upstream to the 2.24 Iv.                                                   compact charging portion rotary                                             hearth                                       (single unit)                                                               Case 4 Sheet-lik Above the raw material Upstream to the 2.33 Iv.                                                   compact charging portion rotary                                             hearth                                       (three units in parallel)                                                 __________________________________________________________________________     (Note)                                                                        "Ex." means Existent example, and "Iv." means Example for the invention  

Case 1 is an example of manufacturing pellets of 20 mm diameter likethat in Example 8 and charging them by a plate type shoot to a rotaryhearth.

Case 2 and case 4 are examples of compacting into a sheet-like shape. Incase 2, a single double-roll compressor of 5 m width was disposed justabove the raw material charging portion of the rotary hearth, a roll onthe side of compression and pressing was disposed at the upstream to therotary hearth and a fixed roll with no pressure was disposed at thedownstream to the rotary moving hearth. On the contrary, in case 3, theroll on the side of compression and pressing of the double-rollcompressor was disposed at the downstream to the rotary moving hearth,while the fixed roll with no pressure was disposed at the upstream tothe rotary moving hearth. The double-roll compressor used was identical(5 m width, single unit).

Case 4 is an example of disposing three double-roll compressors of 1.67mm width in the lateral direction of the rotary hearth furnace in whicha roll on the side of compression and pressing of the double roll wasdisposed at the downstream to the rotary moving hearth, while the fixedroll with no pressing was disposed at the upstream to the rotary movinghearth

In operation, like that in Example 8, the rotational speed of the hearthwas controlled such that the metallizing ratio of the reduced iron was92%.

As a result of comparison for the operation in each of the cases, sinceless impact shock was exerted till the charging to the hearth, thepowder was less caused, the undesired effect due to the deposition ofthe powder in the hearth was reduced and the productivity of the reducediron was improved. Particularly, in a case of disposing the pressingroll of the double-roll compressor at the downstream in the movingdirection of the rotary hearth, and in a case of disposing a pluralityof double roll compressors with a shortened roll length, a higher effectof improving the productivity was obtained.

INDUSTRIAL APPLICABILITY

As has been described above, according to the method of manufacturingthe reduced iron of the present invention, since the sheet-like compactcan be obtained merely by shaping the raw material mixture with rolleror the like, the processing time is extremely shorter compared with acase of granulation such as pelletization and the operation andmaintenance for the device used for the shape are also easy. Inaddition, while pellets are insufficient in the strength as they aregranulated and the strength has to be increased by drying, thesheet-like compacts are not collapsed even not by way of the drying stepby merely placing by way of a support roller or a charging chute on ahearth. If they are exposed to a high temperature in the furnace tosuffer from more or less crackings, it does not lead to collapse andgives no troubles in the reduction. This method can be practiced easilyby using the device for manufacturing the reduced iron according to thepresent invention described above.

Further, the reduced iron obtained by the method described above can becharged at a high temperature state into a shaft furnace or an in-bathsmelting furnace and melted at a high heat efficiency, to produce molteniron of good quality.

We claim:
 1. A facility for production of reduced iron, comprising:amixer for mixing fine iron oxides with powdery solid reductants; acompactor for compacting a raw material mixture obtained through themixing step into a sheet-like compact; a feeder for placing thesheet-like compact on the hearth of the reduction furnace; and areduction furnace for reducing the iron oxides contained in thesheet-like compact fed therein, said reduction furnace being a rotaryhearth furnace and comprising: a furnace body provided with a feedinginlet for the sheet-like compacts, a discharge outlet for the reducediron produced through high temperature reduction of the iron oxides, andan exhaust outlet for off-gas generated therein, a hearth installedtherein so as to be horizontally rotatable, and burners for combustingthe fuel after the fuel and the oxygen-containing gas are blown in,wherein the compactor is a double-roll compactor disposed above thehearth such that axes of the double rolls intersect the direction ofadvance of the hearth at right angles, and the feeder of the sheet-likecompact is a feeder chute.
 2. A facility for production of reduced ironaccording to claim 1, wherein the double-roll compactor and the feederchute are divided into a plurality of double-roll compactors and feedersdisposed in the direction crossing the direction of advance of thehearth at right angles, and across the entire width of the hearth.
 3. Afacility for production of reduced iron according to claim 1, whereinthe feeder chute has a part thereof concavely curved in a longitudinalsection along the direction of advance of the furnace.
 4. A facility forproduction of reduced iron according to claim 1, wherein the feederchute is a tip chute detachable, and attached rotatably around aconnection point as a fulcrum, having the extremity thereof in contactwith the hearth.
 5. A facility for production of reduced iron accordingto claim 1, further comprising a film holder for supplying film togetherwith raw material to the surface of either one of two rolls, and rollersfor supporting as well as transferring the sheet-like compact in thedirection of advance of the hearth.
 6. A facility for production ofreduced iron, comprising:a mixer for mixing fine iron oxides withpowdery solid reductants; a compactor for compacting a raw materialmixture obtained through the mixing step into a sheet-like compact; afeeder for placing the sheet-like compact on the hearth of the reductionfurnace; and a reduction furnace for reducing the iron oxides containedin the sheet-like compact fed therein, said reduction furnace being arotary hearth furnace and comprising: a furnace body provided with afeeding inlet for the sheet-like compacts, a discharge outlet for thereduced iron produced through high temperature reduction of the ironoxides, and an exhaust outlet for off-gas generated therein, a hearthinstalled therein so as to be horizontally rotatable, and burners forcombusting the fuel after the fuel and the oxygen-containing gas areblown in, wherein the compactor is a double-roll compactor disposedabove the rotary hearth, and provided with two rolls, such that the axesof the rolls intersect the direction of advance of the rotary hearth atright angles, with either one of the two rolls covered by an endlessbelt, and the feeding apparatus for the sheet-like compacts comprisesthe endless belt, a belt discharged from the double-roll compactor, asheet-like compact support rollers for supporting as well astransferring the sheet-like compact towards the hearth, and belt carrierrollers for driving the belt.
 7. A facility for production of reducediron according to claim 6, wherein the double-roll compactor, theendless belt, the sheet-like compact support rollers and the beltcarrier rollers are divided into a plurality of double-roll compactors,endless belts, sheet-like compact support rollers and belt carrierrollers disposed in the direction crossing the direction of advance ofthe hearth at right angles, and across the entire width of the hearth.8. A facility for production of reduced iron, comprising:a mixer formixing fine iron oxides with powdery solid reductants; a compactor forcompacting a raw material mixture obtained through the mixing step intoa sheet-like compact; a feeder for placing the sheet-like compact on thehearth of the reduction furnace; and a reduction furnace for reducingthe iron oxides contained in the sheet-like compact fed therein, saidreduction furnace being a rotary hearth furnace and comprising: afurnace body provided with a feeding inlet for the sheet-like compacts,a discharge outlet for the reduced iron produced through hightemperature reduction of the iron oxides, and an exhaust outlet foroff-gas generated therein, a hearth installed therein so as to behorizontally rotatable, and burners for combusting the fuel after thefuel and the oxygen-containing gas are blown in, wherein the compactoris a roller for compacting the raw material mixture supplied onto atilted chute constituted by a belt circulating in the direction ofadvance of the hearth into sheet-like shape and the feeding apparatusfor the sheet-like compact comprises the tilted chute, and a feederchute for receiving the sheet-like compact separated from the belt andplacing same on the hearth.
 9. A facility for production of reduced ironaccording to claim 8, wherein the roller, the tilted chute and thefeeder chute are divided into a plurality of rollers, tilted chutes andfeeder chutes.
 10. A facility for production of reduced iron accordingto claim 1, wherein the feeding apparatus for the sheet-like compactfurther comprises a supplementary transfer belt, constituted by a beltcirculating in the direction of advance of the hearth, disposed so as tobe in contact with the surface of the sheet-like compact beingtransferred.
 11. A facility for production of reduced iron according toclaim 8, wherein the feeding apparatus for the sheet-like compactfurther comprises a supplementary transfer belt, constituted by a beltcirculating in the direction of advance of the hearth, disposed so as tobe in contact with the surface of the sheet-like compact beingtransferred.